'85 GMC Popping & Backfiring when engine is cold!

[chargedstang89]

Ok...I have an '85 GMC 4x4. It has a BRAND NEW 5.7L 350, a brand new edelbrock 1904 carbureator, and a new tranny. Anyways, when I start it to drive it in the morning or evening, it will backfire through the carbureator, the truck will buck...the RPM's will dip waaayyyy down and then it will die out. What is weird, is that it ONLY does this when the engine is in gear under a load. If I put the engine into neutral, it will revv smoothly. It will keep doing this until the engine is warm. I took it to a shop and they put a new EGR valve on it, but that didn't have any effect at all. They also tweeked the carb a little and made it just a tad richer. I can't figure out why the heck this is happening. It just recently started doing this.

Can anyone pllleeeasseee help me????

josh