stumbly acceleration

My '91 XJ is a 4.0L HO 5-spd, and has been running awfull funny lately.
It ran great with lots of power, and then the problem started....this was not a gradual thing.
I went through a couple of moderately easy, though bumpy mud trails with my buddy a couple of days ago. On the drive home I noticed a lack of power when i would step into the accelerator. It almost felt like some kind of driveline drag, except that it was not constant. It starts stumbling during acceleration at about 1800 rpm's, and will randomly run very poorly while cruising.
*I replaced the fuel filter, and the air filter is clean. The fuel injectors don't appear to be leaking, and have very obviously been replaced somewhat recently. I checked for vacuum leaks in a few places, and intend to do a more thorough inspection tomorrow when it's light out.*
if anybody knows what this is, or has an idea what it could be, I'd love to hear from you.
thanks

Bad cat? Easiest way to test is to disconnect downpipe at the exhaust manifold. But first check connections like spark plugs, coil, ect.

maybe the distributor got wet. pull the cap and see if its damp. if it is, spray it with some wd-40 and wipe all the water out.

Try the throtal postion sencer

My money is on the CAT.

thanks for the quick replies guys, I'll check the cat for sure. But, would the cat cause a constant power loss, or would it be random/occasional? bc the stumbling/power loss is not a constant thing. I will also check the cap/rotor/wires tomorrow, I just ran out of daylight today.
thanks again for the feedback, this site is awesome.

My personal experience with a bad CAT did not include stumbuling, only huge loss of power. In the morning, with a cold engine/exhaust, acceleration seemed normal, until the CAT heated up. Seems the pipe internal to the CAT would warp with heat, cutting off exhaust flow, leading to my inability to get above 45 or, as I recall. I was in Canada, camping at the time. Lucky to find a shop in the middle of no-where who gutted the CAT; all was well after that.

yeah, this feels kinda like a fuel staration issue, which is why I tried the fuel filter. The injectors are brand new. I don't believe the pump is the problem, and before I spend $100 on a new one, I thought I'd see if anybody had ideas what else it might be.

A plugged cat acts like a fuel starvation problem, but without bucking, or misfiring caused by a lean mixture. I'd put a fuel pressure gauge on it and insure proper pressure and regulator function. When you accelerate, vacuum drops effecting increase fuel pressur via the regulator, which is controlled by engine vacuum.

how many miles do the jeep have. O2 sensors can go bad in a hurry and really screw up acceleration and cause stumbling