When driving my '85 IROC (with an aftermarket 700r4), I have noticed a "hesitation" around 40-45mph. I have stared at tach when this happens and it does not budge so I'm guessing it's not an engine issue(?). This is a recent trans/motor swap from a wrecked car (although the trans has not been separated from that engine since its installation over 10 years ago). Any thoughts on what this may be (transmission or otherwise)?

 

hey did you ever find out what was wrong?? my car shakes at 40 and feels sluggish and my tach is stagnant then i punch it and it moves at 2k rpm help yo!