Rudecaddy

I have a 1961 VW beetle with a '99 LS1/T-56 combo. Previously I ran a '95 LT1/T-56. The car has the factory Camaro computer, with no EGR and currently no rear O2 sensors. I have put about 300 hundred miles on it since I got it running, and the only real problem I have had it the engine will sputter under very light throttle shortly after startup, or after the key has been cycle, it clears up within five minutes and runs great. Could this be because of the rear O2's or EGR? Otherwise, all wiring is good, and the computer holds memory with the key off. Any ideas here would help.