well I've been home from college and decided to work on the truck. The engine is a built 400 sbc, everytime I run the engine I get a very loud backfire from the driver side header. I am running open headers, I have tried adjusting the timing and the idle but nothing really happens, and when the engine is under load the backfiring gets worse. How do i stop this from happenning? I think its the valves so I'm gonna pull the valve cover tomorrow. Also I just installed a new torque convertor w/ a higher stall(1500-2500). And now the truck is barely moving, it may be losing power due to the backfire trouble, what all should I check out on the tranny and transfercase to make sure everything is up to par.