different 318 question

I know its not a mopar but i had a bronco 2 that did the same thing with a 5spd trans. it would pull well up to 3 or 4k rpms then just go flat. Unknown mileage on the engine. I advanced the distributor and it picked up really well. It pulled great thru all gears and improved fuel mileage. The only thing is it put the timing strobe clean out of range on the harmonic balancer. That told me the timing chain is stretched pretty bad. If your chain and gears are stock and havent been replaced, and you try this and it picks up, I would check your chain and gears.