need some tuning help here... 85 W350 crew cab, 360 auto.
Truck runs and drives great in normal everyday operation. The problem is when under high load trying to get moving. It just will not move. Engine bogs down and holds idle speed, may quit, but most of the time not. Never see any black smoke when its stumbling. What could cause this?

Truck is mostly stock. I added the 302 casting heads to the stock bottom end, has an older performer intake, and a 9801 aftermarket Thermoquad..I know Thermo bog... Ive used these before with great success on other trucks. Could this be just too lean? ignition issues? Any help or thoughts would be great, Thanks to all.