360 trouble. please help

I have a 74 340 with a mild cam and 4 barrel eldlbrock intake i bought last year. It hada holley vac secondary that was giving me alot of flooding problems and back fire so i put on a new edlebrock mech secondary. Still having back fire issues so im thinking it wasnt the carb. If the car is in park it will rev up no problem. If i attempt to drive down the road the motor leans out and pops at high rpm like right before it shifts.