I have a 96 f350 7.5 l auto, truck won’t drive forward unless you start of manually in first gear and shift manually... no problem in reverse. Sometimes truck will act normal but usually if you try and start off in drive it’s like your trying to start off in 5th gear or something

 

Did you notice if the OD light on the shift lever is blinking?

 

It is not flashing

 

Some systems are designed to prevent damage with full power applied. Called Limp Mode.
Don't know if this is what might be happening, but might be a good idea to have vehicle checked for pending/ codes in memory.
If any codes are present might provide some direction as to where to start checking.