I have a 1990 gtu with turbo conversion. it also has coil overs and 17in tires. when trying to take off from the line sometimes it tends to hop the *** end at bit. Is the problem bad diff mounts or the in the rear end? the mounts look to be in good condition, no cracks or wrinkles.

 

No. Its usually blown rear sturts. If your rear struts are stock, they are likely blown or completely worn out.
Valving too high and extremely high rear spring rates will also cause rear wheel hop on launch.

Bad diff mount gives a very audible clunk under hard clutch dumps.