87 ford 150 will not accelerate past 3000rpm when under load

Ok i have a 1987 ford f150 4x4 with the 5.0litre engine automatic transmission. Whats happening is the truck has no power i drove it a distance of twenty miles and could not get it to go past 45 mph unless i was going downhill. The engine seems healthy when it doesn't have a load it revs good and idles nice. However to drive is a nightmare i had to have my foot to the floor the whole time to get it to stay at 45mph. I have tested my throttle position sensor, throttle air bypass, and map sensor and they are all working properly. I also tried testing my fuel pressure but the schrader valve is bad so i saw i was getting fuel flow to regulator and decided for the 18 bucks at autozone i would take a chance and replace it to see if it was a fuel delivery problem but still had same sypmtoms. I am possibly thinking next maybe a clogged converter or bad egr valve but am looking for more suggestions. Also it has diffucultly starting