tires don't wanna spin after gears

[da89cup]

I got 4.10s put in with new clutch friction discs, friction modifier, all new bearings, & I can't do doughnuts. I have an 89 coupe with a 5 speed. When I just bought the car with 2.73s I could do all the doghnuts I wanted, but eventually I couldn't do them anymore because of the clutch discs in the diff (so I thought). So after rebuilding the diff & putting in 4.10s I thought the problem would be solved. I still can't do doughnuts. They start to spin together but when I try to go into the fishtail the car doesn't fish-tail. What the hell is going on? I have myself on tape at the track doing a burn-out & only one tire is spinning. The owner of the shop who did my rear end said this is normal. If it's normal how come I could do doughnuts before & now I can't. Please help, it's very frustrating spending that kind of money & you still have the same problem. Thanks in advance.


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89 coupe, 351W, 351W heads, 30lb injectors, 190lph pump, 80 maf, 70 tb, ? cam, cobra upper, gt 40 lower, 4.10s, (14.594@96.97)