There's so many things it can be, When I put in a new t-5 for the second time, i had one like that, and it turned out to be the flywheel. As of now, I am experiencing the exact same thing you are, but I am going to go the route the others have listed first before messin with the flywheel!
Good luck!
------------------
Joe!
1988 GT, 167,000 miles!!! 13.71@105mph Check out my listing!
Click here! Or my website:
www.joe4speed.com
1999 Ninja ZX-6R 10.32@135mph!
1993 Olds Eighty Eight LSS