Kind of curious as to what could cause my current issue.

Put a carb back on my 440 in the interest of getting it running again.

Truck starts and idles fine (albeit a little bumpy, but it always did). AFR is right around ~14.5 at idle. It'll rev quickly in park and doesn't seem to have any issues.

During the pre-drive tuning, the truck was idling on it's own and I heard a loud "POP", the truck dropped it's idle to around 200, almost stalled, sat like that for a couple of seconds, and the came right back up on it's own. Kind of odd.

Transmission is recently rebuilt (less than 300 miles on it) and ran fine before the carb went on (previously EFI).

When I shift into drive and start moving forward, the engine doesn't seem to want to rev, and if I force it, it'll backfire loudly and lurch.

I'm not sure if I'm redicously lean and rich, as I know an O2 sensor can be fooled in the extremes of either situation.

My kickdown is properly set and operating.

My Edelbrock 1406 has the IMS turned 2.5 times out.

Is there anything I can do to try and figure out if this is engine related or transmission related?

Thanks all