i have a 350 with an automatic turbo350. the engine idles fine in park and it accelorates fine too. once i put it in reverse or drive i have to give it significantly more gas just to keep it idle and if i give it enough gas to actually move the car it backfires and kills the motor. any ideas?

parking brake on? just a WAG....

vacuum leak

Timing??

What is the idle RPM? Correct me if I'm wrong, but it should be 500 in gear (obviously, it takes two people to set it, one behind the wheel holding the brakes on while the trans is in drive, and one adjusting the idle screw to achieve 500 rpms on a tachometer). This ASSUMES that the timing is set correctly, there are NO vacuum leaks, and that the carburetor is good.

check your timingv vacuum leak is another good possibility