Engine bogs down around 3000 RPM

A few weeks ago my car started bogging down around 3000 RPM. It would act perfectly
normally until it hit 3000 RPM, then it would hang at 3000 for a second, then start fluttering and
jerking down to a much lower rpm.

I confirmed that the catalytic converter wasn't the issue, then I sent it to the shop. They replaced
the cam shaft sensor, crank shaft sensor, and all the spark plugs and spark plug wires.

I got it back and it drove fine for a while, then started acting up again. I've been driving it like this
for a week or two, and as long as I accelerate slowly I don't have issues. I have noticed that it
will run at a higher rpm before having issues if the engine is hot; that is, when the engine is cold
it starts having trouble at 2500 rpm, when hot it may run up to 3500 before running into trouble.

Any idea what the issue may be? I can't afford to just replace everything blindly, I'd like to do
some troubleshooting and figure out what the problem actually is before I start buying expensive
parts. Thanks!

tl;dr engine loses power and rpm becomes erratic above 2500-3500 rpm, depending on engine
temp. Already checked cat, cam and crank shaft sensors, and spark plugs.