I have a 1990 cherokee with the straight 6 and 5 speed. I was driving it one day went to shift into 2nd gear at 4000 rpms. I heard a loud noise. I took it to a mechanic he check all the scenser andf there all good, but it still dont go over 2000 rpms without bogging down and popping. I can drive it but i have to shift early to do that.Anyone no anything?

 

Could possibly be a bad coil, maybe a fuel pump.

 

Bad plug wires can cause what you described under a load.