Slow, slow, then it just freezes

My apologies if I’ve wandered into the wrong subforum or if I'm asking something that’s been answered a thousand times already.
I've run into a bit of a wall.
I'm on a Verizon connection, clocked at about 4 Mbps. Here's the kicker: when I run a speed test, the numbers look perfectly fine. My hard drive is mostly empty—only about 30% full—and Kaspersky says there isn't a single virus in sight. RAM is plenty.
I also run CCleaner regularly to keep things tidy. On paper, everything looks totally fine, which is why I'm stuck.
This sluggishness is driving me absolutely insane. Trying to load a site like the New York Post can take a full minute; sometimes I can't even get the LA Times to pull up, or even Google.

🤔

What should I try next? Where do I even start looking to fix this mess?
Thanks in advance.

So, which browser are you currently running? If you don't have Chrome installed, maybe grab it just to see how things behave there. Honestly, it might be worth downloading Malwarebytes as well—just to run a quick scan and get a second opinion. It’s always better to have that extra bit of peace of mind knowing your system is actually clean, right?

Firefox.
Alright, I'm going to give Malwarebytes a shot.
Thanks.

Oh, and yeah—I don't even touch Internet Explorer anymore, but I know it’s infected with that damn sweet page hijacker that I just can't seem to shake.
Stupid question here: could that mess with my other browsers too? Even though I don't actually use Explorer?

I’m not entirely sure, but you might want to grab AdwCleaner and run a scan with it—it’s specifically designed to wipe out those annoying toolbars and all that other junk.

It just wouldn't work. Eventually, I lost my mind, moved all my critical files over to the D drive, wiped the C drive completely, and did a fresh install of everything. Now? It’s flying.
thanks for the advice