I don't really know where to start on looking at this problem, what is happening is when I'm in 4th gear and I speed up to say 60 or more and then let off the gas to coast and then put back on at any speed less than what I was going but more than 45ish it has a big clunk, and jerks the car, I already had the transmission mount replaced and checked out since it was replaced since this problem has happened and its definitely not the transmission mount, does anyone know what it could be? I had my transmission rebuilt about 2 years ago/10,000 miles ago its an 86, 700r4, limited slip diff.... any guesses would be helpful even..

 

torque arm mount , or maybe a u joint , maybe slight chance it might be a motor mount . hope this points you in the right direction.