Alright...

I start up the engine and everything is okay. I put it into reverse and the truck jerks hard, then I can go in reverse.

I put it into "drive" and I can accelerate to about 30 mph before you can feel the engine starting to run harder than it should in drive mode and at that speed. I don't know how much faster I could go in drive mode and I haven't tried because I don't want to mess anything up more if something is wrong.

I can put it into 2nd gear and go around 45 to 50 mph with no problems but if I try to go faster than 50 mph you can feel the engine running harder than it should as I accelerate.

I don't know the first thing about a vehicle and I have no idea what to do.

 

Howdy and welcome!

First we need some more info. Engine and tranny for one.

It will either be a C6 or AOD auto tranny. Check this page to figure out which one.

https://www.f150online.com/forums/sh...d.php?t=211867

Adrianspeeder

 

I'm assuming it's this one because in the display panel it has "d, 2, 1" in the truck.

Model: C6
Type: three speed non electronic
Years: 1980-1991: F-Series, Bronco
..........1992-1997: F-2/3/450
Engines: 300, 302, 351, 460, 6.9L, 7.3L
Display: PRND21
Ratios:
1st 2.46:1
2nd 1.46:1
3rd 1.00:1
Trans code: G