I have a 94 Wrangler, 4.0 liter 5 speed....Recently it started running odd...about 2000 rpms, in 2nd gear it shudders, like a fuel cut off or something and doesnt want to go above 2000 rpms, until I shift to 3rd.  In third gear I can get to about 60 mph around 4000 and it does it again. 5th gear I cant go above 70 mph. some times, if i am going slow in first the same thing happens at 1000 rpms. then it will backfire into my intake box. at the same time, my oil pressure drops when it starts to act like this. Ive replaced, the O2 sensory;distributer cap, rotor, plugs and wires 3 times.. and today replaced the thermostat. I am thinkin its the fuel pump or filter but dont want to spend anymore money unless I am sure. Also as all this happens I get no check engine light.. Any  ideas or help is greatly appreciated.

Thanks,

Calvin.

I'm no expert ... but here's what a quick browse of the web found.  It could be any of these, or something else:

cam sensor, valves, vacuum hose, worn timing chain.

Pete  

ok, but something I forgot....when I am driving and this starts happening, If I turn my jeep off, and start it again, it sometimes corrects itself for maybe 10-15 miles....and it normally doesnt start acting up for 20 or 30 miles...or till the engine gets up to operating temp...

Calvin.

im only new to the jeep game so im not sure if they have one, but it sounds like a "crank angle sensor" all it does is tell the ecu when the engine is at top dead centre, it is a common problem in many early skylines, that run rb30's.