What's a fair way to step up the towing power of this throttle body injected 318 without spending much cash?
My sister's BF is trying to use a 89 D150 for towing his sprint car. Despite the light weight of the car the truck simply can't handle the load. There's one hill on the highway they have to drive around because the rig drops to 45 mph with his foot flat on the floor.

Is there any gain to be had by ditching the TBI and stuffing an intake and carb on the little engine?

I thought about finding a rear end at the salvage yard with some steeper gears but I don't know what it has now.

I'm willing to help him put it together but he has exactly ZERO bucks to spend on it.