1995 Mercury Villager Won't accelerate

I am having the exact problem with a 1995 olds 88. I recently put an engine in it and have gone through the entire fuel system, (pressure is up to specs), every sensor on the engine, as well as pulling the fuel and ignition wiring harnesses back out of the car to inspect them. I am getting no trouble codes now and as you said great idle characteristics and plenty of pep if you floor it, but practically nothing in between. This is not an intermittent problem, so I'm not thinking it's the computer. I bought the car with a blown engine and don't know if this problem is attached to the car or the junkyard engine I installed. I do this for a living and rarely find myself at a loss, but when I do it seems very difficult to come up with the correct answer.I know that 1995 was the transitional year for the OBD2. I could have installed a faulty sensor, but I need help narrowing it down and I am praying that it's not the computer! Someone HELP! I've almost had enough!