1995 Riviera non s/c wire harness MAP sensor?

Hi I bought a 1995 Riviera which had a bad engine, swapped the engine out, now the traction off/service engine lights are on and when I go from complete stop to takeoff, its slow and takes time to pick up speed. At first it was the vacuum line came aloose, fixed, but now its still sluggish. I had a guy tell me since those two lights were on, most likely it was a EGR or idle sensor gone bad on the harness and I need to change it...the PRND123 on the dash cluster also blinks 3 or 4 times once the car is started and put into drive as well. Any clue as to what could be wrong, or what would make it so sluggish? Once its around 30-40 its fine, but twice I had it at 80mph and once it hits 80 it automatically slows down..waaaaaayyy down, to like 40. Not cool on the freeway. Its like a governor kicked in or something. But he said all that might be from the electrical problem with the sensors. But he doesnt really know, hes assuming (he works at AutoZone). I figured Id ask a broader base. Would it be easier to simply change out the entire harness? Thanks

Hi I also noticed that when we did the motor swap we hooked up all the sensors/plugs but on the passenger side in front of the alternator where I believe its the MAP sensor? There was no plug to go into that on my harness, which came off the original Riviera motor. Should there be a plug in there? I couldnt imagine why not. Ive had three people, 2 being mechanics tell me that since GM used a 3800 in like 10 models of car, not all took that plug therefore if it wasnt on the original harness, you dont need it. Im thinking maybe this has something to do with the sluggishness of the car from takeoff? Its really disgusting. I like to step on it and get that 'jerk' like my GP used to, but this one is like old lady slow. Should I get a new harness and plug that sensor in?

Your two threads on the same subject have been merged into this thread! Let's try to keep threads of the same subject in one thread. Duplicate threads are confusing and frustrating to read and respond to. Your cooperation is much appreciated.