[milner351]

a buddy just went through this nightmare in a mustang with a C.
A second custom ground roller cam later, he realized that you have to run the right distributor gear with a roller cam....

I drove tens of thousands of HARD miles on a C powered '70 mach1 with a trw hi volume pump and NEVER had any problems.

First do you have a roller cam which requires a bronze distributor gear? If that's not the case, if you have not already, put in the billet drive shaft, the stock hex shafts are just too fragile for a hi volume pump or a high performance engine.

Check the engagement, is there any end play between the dist and cam gears? Is the cam gear worn out / galled / damaged in someway?
Make sure you are not bottoming the dist gear in the block, shim if you need to, check the block bore face, and the dist gear carefully to see where it may be binding / heating up. Is the wear across the distributor gear teeth even or are they worn more at the top or bottom.... etc.
Good luck!