engine RPM fluctuates under load
 

I hope this post should go here,at any rate I've got a 93 Cherokee with a straight 6 4.0L that has been having a lot of trouble whenever I rev the engine over 2000 RPM or so,I've checked the fuel lines (filter,injectors,fuel pump and fuel regulator)replaced the spark plugs,spark plug wires,distributor cap and rotor)and I've checked the air filter and such and I still can't quite figure out whats wrong,though I've been told at this point it's very likely to be a transmission problem,also when I checked the fuel pressure it was at 30 PSI when the engine was running,not 100% sure that is what it should be so I could use some help on that as well