Overheating causing stuttering

Core 2 Quad, 8GB RAM, GTX 750 Ti, 550W power supply
After about thirty minutes of playing GTA or Assassin's Creed Unity, the stuttering becomes unbearable. I suspect overheating is the culprit.
The CPU is running a $50 cooler, the GPU is using its stock heatsink, and everything is housed in a massive, open-sided metal case.
My assumption is that I need a new chassis with decent airflow and perhaps a more robust cooler for the graphics card, though losing the warranty is a frustrating prospect.
Please offer some suggestions, provided they are budget-friendly.
Thanks

What kind of temperatures are we seeing for the CPU and GPU under load (stress tests or gaming)?
You definitely don't need a second cooler for that card; the one you have is more than enough...

If I recall correctly, you had a thread where your Core 2 Quad was hitting temps above the recommended limit—it might be thermal throttling and downclocking to something like 1.3 GHz, which would explain the stuttering.

Which specific cooler from $50 are you talking about? Give the cooler a good cleaning and swap out the thermal paste—check this link

Last time, we fixed it by leaving one tiny corner of the CPU ungreased, which caused it to overheat; once everything was properly coated, it ran fine. If I recall correctly, the thermal paste was replaced about three weeks ago.
The cooler is an LC Power—I can't be bothered to hunt down the exact model right now, so I just listed the price; I believe it's an LL 95 or something similar.
Would it make sense to swap out the case and add another cooler?
I'll run these tests and let you know.

Which software was I using again? I tossed everything from my computer straight into the trash.

Try running OCCT for a stress test. Your CPU max temperature should hit about 62°C, but also keep an eye on the clock speed graph. Check if it starts throttling—dropping from 3.2GHz (or whatever your base is) down to something like 1300MHz once you put it under load.

It shouldn't be overheating just because the corner of the IHS wasn't perfectly covered in paste (check out this video); the cores are located right in the center anyway.
What kind of motherboard are you running? You might be hitting thermal throttling because the board itself is junk—it probably can't handle a 125W CPU under full load.

I know using a spatula doesn't make much sense here, but it did the trick, so I wasn't complaining.
The motherboard is a Gigabyte GA-970A-DS3.

The motherboard is solid enough; it really could have benefited from some active cooling, but it gets the job done. You should probably run a check on those temperatures yourself.

The CPU stays steady at 65°C, while the GPU hits a solid 3415MHz and maintains 60fps during gameplay. However, once I minimize the window, the GPU clock speed drops to about 800-1000mhz and the frame rate tanks to 15-20 fps.

Your CPU temperature is way too high. It’s especially concerning if you hit those numbers within just a few minutes of booting up; ideally, if you’re running it for 24 hours straight, you shouldn't be seeing anything north of 62 degrees.
Who installed the cooler for you? There's a chance it isn't seated properly, or maybe someone went overboard with the thermal paste...

I just applied it by hand with my finger. Honestly, I think that might be the issue; whenever I tried using a single grain of rice to spread the thermal paste and let the cooler's base flatten it out, it would always overheat. I'll probably have to try using one of those plastic spreaders instead.

If the cooler base isn't making direct contact with the CPU, no amount of thermal paste is going to save you.

The cooler is tight and performs basic tasks.
I am truly at a loss for words regarding how awkward this is.

Try underclocking your CPU and see how it performs while gaming.

Gregory Hayes87 said:I did it solo using my finger to spread the paste—honestly, that’s probably the issue. Every time I dropped a single grain of rice's worth of paste onto the center and let the cooler's weight spread it out, it ended up scorching. I’ll have to try using that plastic spreader tool instead.

Finger spreading technique🤣

People have become obsessed with this "grain of rice" method. It used to be people talked about a pea-sized amount, or even a bean, or just a thin line. Seriously, just watch the video; it breaks down everything, including the pros and cons of the different methods.

You also have the option to undervolt the CPU while maintaining the same clock speed. For instance, a Phenom 955 can hit 3.2GHz at 1.175V in the BIOS—though, of course, that varies depending on the specific chip and the motherboard you're using. This is generally the case according to this source. But before you dive into that, definitely double-check your thermal paste application and make sure it's done right.

I applied just enough to cover it, then ran a test at 185°F where I spread it on like Nutella—to use a bit of hyperbole—and now we’re sitting at 144°F.

Yes, it’s clearly an issue with the amount of thermal paste being used and your application technique. Honestly, instead of spreading it manually, you're better off just applying a dollop and letting the heatsink do the work—that way you avoid those pesky air bubbles. Just make sure you thoroughly clean off the old residue before you start a new application.

Back again with my temperature grievances,
One of the screws on the cooler stripped out and is loose, so it keeps bumping against the processor, though it isn't clamped down tight.
I wasn't about to be lazy, so I headed down to Best Buy yesterday and picked up $67 a Zalman CNPS5X. The temperatures are excellent—they don't even cross 55°C after ten minutes of OCCT testing—but the cooler itself is unnervingly loud. The box claims 20-32 dB and boasts "ultra quiet" performance in five different places, yet here we are. It’s spinning at 2150 RPM and sounds like a jet engine taking off, which is a problem because a silent PC is a priority for me. My previous LC 95 cooler was genuinely silent. I plan to take this back to the store and swap it for something else. Should I look for a specific model, or just demand a refund and fix the screw on my old one?

Look

I told you those temperatures weren't going to cut it for an aftermarket cooler.

You picked up a subpar unit for $67, and honestly, the cooling performance is barely hitting the level of an LC-CC-95 (assuming it's actually working properly 😁), if not even worse—plus it’s louder. If you got the first one, I'd suggest returning it for a refund. If you can swap it out, just grab the LC-CC-120 instead. It’s hands down the best value for the money you'll find in the States right now.

EDIT

as long as your case can accommodate a 152mm clearance

I’ve had this first one for about eighteen months, but I am absolutely returning the second one.
1. Does the refund process actually work under these new consumer protection laws regarding the two-week window?
2. Which model should I go with instead, since they don't carry the LC-CC-120 at Walmart?

Actually, the LC-CC-95 comes with a 2-year warranty, even if you pick it up at Micro Center.

By the way, why limit yourself to Micro Center if you’re living in NYC? They absolutely hammered you on that Zalman unit... You have certain consumer rights when buying remotely—I believe there's a 7 to 8-day window where you can return items; otherwise, you're basically relying on their goodwill. At least, that was the rule until recently.

If you're dead set on Micro Center, grab the Zalman Optima for $94, though honestly, it's a poor value compared to the LC 120 series. The price gap is huge, yet the Optima is nearly twice as expensive. Their selection and pricing are pretty lackluster.

EDIT

Of course, that's assuming your warranty claim for the LC 95 actually gets approved, or if you just decide to stick with the same model because the Optima feels like too much.