HELP WITH CHEVY 4.3

I have a 92 chevy k1500 with the 4.3 v 6 when i am driving it it seems to have no power and you can see the tach jump(twitch up and down) when I take it to almost red line then it jerks and i get power back but as soon as i do i need to shift (manual trans) also if i hold rpm steady my shift light comes on even if i am at 2000 rpm as soon as i let off or give it gas it goes off cant figure out what the problem is any suggestions? i have replaced the following
map sensor
electronic spark control module
throttle position sensor
o2 sensor
fuel pump filter
egr valve
throttle body
egr solenoid
injectors
distributor
vapor canister
cap rotor
ignition coil
computer(has hypertech prom)
spark plugs

tried plug wires? I had my old s10 do the same thing to me

plugged cat?

Make sure your battery is 100% good, have had a few s10's and blazers over the years do the same thing. May seem odd but a bad battery was the problem.

Make sure your grounds are good. On this truck I think most of them are on the thermostat housing. there may be more on the back of the R cylinder head. Make sure there are no broken wires & everything is clean & tight. Bad grounds will cause all kinds of goofy electrical problems. Good Luck!

I had a toyota once do a similar thing. It was a combo of a bad ground wire on the motor and a bad wire inside the wiring loom to the computer.

Check the knock sensor, mounted in the block by the starter bad sensor or wire can cause est to make timing ****** and do crazy things

I guess the word for the opposite of timing advance wont print on here