just fitted a tail shaft loop and took it for a run about 20 mins into the drive the car is now surging between 2500rpm and 3500rpm uner light to mid aceleration the surging is not real bad but feels like a few bumps what could it be? 94ef

When your refering to "loop" what you refering to?

Just a guess.

When you had the tailshaft out, did you make sure the tailshaft uni joints are all freed up. Problems can occur when you replace uni joints and you don't make sure they are working properly.

Alot of the time you have to give the area around the uni joints a tap with a copper mallet to free the new joints up.