Chevrolet Repair: motor shake, vacuum leak, input shaft

Question
I have a 79 suburban w/350eng/thm350tranny,np-203t.c i recently replaced tranny,transfercase and flywheel with donated parts (used). between 1500 and 2500 rpm i have a violent shake/vibration in drivetrain or motor.in any gear park or neutral. even with the torque conv. disconnected and engine turning free of Trans. after 2500 or so rpm it smoothes out,also it seems when i accelerate hard. before switch this did not occur. i did not notice any cracks or otherwise in flywheel before i put it on, and i dont notice any wobble in flywheel while engine is running  

Answer
Hi Robert,

I know it is off base, but how about a bad wire?  You could have knocked it off during the install.  Or broke it.  If you don't think that is it, I have to go with bad torque converter.  Possibly an out of balance flywheel.  Usually a vibration is bearing in torque or maybe the input shaft.

How about a vacuum leak?  

C J S