87 B2000 Engine Vibration

[19k40rocky]

I got a used engine out of a salvage yard in Colorado recently to replace my other engine that suddenly had a knock and bad compression on one cylinder and turned the antifreeze black and oily. Anyway, the new engine has a mild vibration to it starting around 2000rpm and keeps it up through the RPM range. Pickup really doesn't want to go past 70 mph and makes the steering wheel feel like you are hanging onto a vibrator. It has 140 compression on all the cylinders. Vacuum gauge holds 20 inches steady. The pan looks like it has been taken off before as it has orange form a gasket on it. I am wondering if someone had this thing apart and turned a rod around backwards or something. If it is could I unbolt the rod and turn it without messing up the rings? Not really excited about having to pull this engine back out. I had called the salvage yard I got if from and they told me to change out the harmonic balencer. That didn't work either and don't think they are going to stand behind this engine. Any ideas for a out there?