94 GMC Safari Acceleration Issues

Hi I need your help experts of Gmc's.  I have a *94 gmc safari sl 4.3 v6 mini van. Only 71k + miles by the way ill sell it for 1,500 as is.  It's having acceleration problems. Basically it all started when someone changed my water pump. I know it has nothing to do with it but recently someone told me there is a sensor behind it that regulates all sensors and if dirty can lag acceleration. Anyhow here's the issue when the car accelerates from 0 to 40 or more it lags and is no accelerating properly. I have to keep pushing the pedal tapping it faster and faster to accelerate it.  This comes and goes meaning sometimes it is normal but more often than not its lagging. When i turn off the car quick and turn it on it goes away but the acceleration is hardly the same as it used to be anyways and accelerates slower than normal. Once in a blue moon it goes back to normal the way it used to be.  Someone told me because when i turn it off and turn it on and it accelerates almost normal to normal sometimes that it has to do with the oxygen. Now im not a car expert but here's what ive tried and figured it could be been trying for months now. Had the fuel filter changed not it, had the fuel pressure checked not it, Fuel pump not it, catalytic not it. The mechanic who changed the pump said it was something oxygen related now how would he know that? I think he sabotaged it to get more money from me i haven't spoken to him since he disappeared. I think its either the throttle body part or whole thing spiders ect. Or its a bad wire somewhere its a pain to find i hope not. Or its the o2 sensor let me explain. I had a diagnostic with an obd1 sensor. The corporate office from GMC after many calls and hit a wall with an evil woman who thinks i wont find the upper vp's numbers i will eventually or if someone has it they are located in Detroit michigan has impeeded my progress for answers but according to them and others it doesn't have many sensors. Doesn't have a map sensor but im not sure about that. The obd1 test from someone who had the old red machine obd1 where years before 96  car parts compatible from 91 to 94 only i believe that's what corporate said not anything after 95. Anyhow the obd1 test said it was either the catalytic, fuel filter, or o2 sensor. So far the only thing i haven't changed or checked is the o2 sensor will do that this week finally been busy doing other things. someone told me on rare occasions the o2 sensor rd cause acceleration  problems. several mechanics said no but we will see. At this point any suggestions would help. Oh yes an my other theory is that its the computer. I had it changed a year prior after a questionable mechanic shop told me i needed it after battery died. Found out later after battery died how cheap and easy it is to change only 100 bucks or less and its plug and play. Was charged 400 bucks. Went back for warranty the guy said he lost my records. Will consult lawyer i think that's illegal he must pay but anyways don't worry ill rate him badly on Angies list for that prick.  Any help would be greatly appreciated. I'm going to try to post this in as many sites as possible. Ill keep you guys updated on my o2 sensor change. Don't want to spend too much money on this otherwise i would have changed all my theories already.  wb asap and please logical helpful replies and if you don't really know don't answer its already confusing enough.