If he problems arose immediately after the t-belt was replaced it was likely installed wrong, however if the issues began after sometime, it is likely not related to the t-belt.

Have you put a timing light on it yet to see what if the timing is correct?

Any white smoke on start-up, does the exhaust smell like gas or is it sweat smelling?  Loosing any coolant?  If you have the beginning of a BHG, you could have rad fluid leaking into the cyls over night this would cause it to start/idle rough until the fluid was gone.