1. When did truck come home from shop?
2. How many drives/miles since coming home from shop?
3. Was gas in tank those two years?
4. Backfire is not a symptom of fuel shortage. It's a symptom of too rich or no. 5 issues.
5. You may want to check plug wires for cracking, distributor cap crack, timing if you can, choke operation, idle speed, vacuum hoses, carb hold down fasteners.
My current best guess.
You did say you smelled gas= Scenario of: carb sending too much gas to manifold.. backfire.. flooding then stalling, waiting for drain off, restart, re-flood.
Which possibly is:
Carb float/needle valve not shutting off gas or wrong/too strong/"custom" fuel pump.
This is more likely than timing but there is Murphy's Law to consider.
What recent work done?
I have read where "backfire", better known as spitting/sputtering/coughing fit thru carb, can be too lean....but so far you say tail pipe. Aye? Bang bang shotgun pow!?
