1991 Chevy 2500 350 cu in auto trans stall only in reverse
 

Truck runs great but most of the time, not always it seems to starve during backing up and stalls

Tps sensor or something within the intake sensor. Like maf... Usually when the intake is working and has a fuel mixture... The truck would regulate for the added weight from transmission. When there's vacuums the truck would stall and loose power. If not then is fuel pressure. If not... Then transmission solenoids. But most is the air fuel mixture