no power when warm

My Jeep runs fine when cold. Revs freely through all gears, acceleration is strong.
When warm, it has no power from about 2500 to 4000rpm. It will hesitate between 2500 to 3000, then nothing.
Someone suggested a bad cat. Why would this not affect cold operation?
It's an 88 with 4.0 and AW4.
Thanks.
Jim

I had a similar problem with my '89. It turned out the vacuum operated valve at the mouth of the airbox was shut closed after it warmed up. It's supposed to be closed when the engine is cold and opens up as the engine reaches operating temp. So when it stopped operating properly on my Jeep, the intake received only hot exhuast air. Simple check: once engine is at full operating temp, take a look at this valve to see if it's blocking fresh air from entering the airbox.

Tom

not it

I haven't had that valve for years. Couldn't be it, but thanks anyways.

FYI, it appears to have been the cat.