Hesitant Engine

I have a 1990 cheyenne with a 4.3. It has a horrible time getting off the line. I slam it to the floor, and it doesn't peel out like every other 4.3 I've ever seen. Also, it is a dog up to about 18-20 miles per hour. It normally shifts around 25-28 mph. It's not that shallow of a gear, I'm just a little bit of a leadfoot. First gear will go to about 35-37 mph, but anyway, it just hesitates up to about 20 mph. It doesn't matter how much gas I give it, it just sits at about 1250 rpm's. anyone have a clue?

Looks like ol Twink needs to get Fordatised...