I have a 72 C20 Big Block truck complete with the 3.54 Dana 60 Rear end. I just got the motor rebuilt, and it runs great except for a vibration in the rpm range of 1750-2000 rpms. The motor runs smooth before and after that, I talked to the machine shop the did the work, and they said it most likely ignition related. Any Ideas from you guys out there.

Oh and it does have a mild RV cam in it, this is my daily driver/work truck!

Any insight would be greatly appreciated.