1995 GMC Sierra 1500 5.7 liter

Old OBD 1 system, could be anything from a loose ground to a computer getting ready to fail. So first check for any codes before you do anything with power or grounds, if there are any codes write them down, then check and clean all the sensors grounds, computer grounds, battery to engine, engine to body, etc. then run diagnostics on those codes, and fix the components or whatever is wrong. Then clear the computer and run the drive time protocols and see if the problems have cleared up. If not then it time for pinpoint testing and that can get expensive. All of this is assuming you have a basically sound engine and transmission.

does the engine rev up, just does not go faster or does the engine not even rev up. Watch the tach when stepping on gas. If tach goes higher but speed stays same, you have transmission issue. If tach does not go higher when stepping on gas could be TPS sensor or clogged exhaust i e bad catalytic converter.