340 Chugging instead of Reving

Locked distribtor and immediately saw/heard an improvement. Took the rpms I to the 5000 range but got some popping out the exhaust. Changed the timing from 32 thru 38 and the popping stayed. I then watched the timing light while increasing the rpms.and it retarding as the rpms increase. When locked at 34* the timing goes down into the 20s. I believe the only thing that could cause this is the ignition box. Any other thoughts before I ship the box out tomorrow????