1989 d250 won’t start
 

Truck will power interior up when key is turned but will not start in park will start in drive but that’s it

I would guess neutral safety switch is on it's way out. Does the shift lever still feel like it's got the detents for all the gears?

Sounds like worn or mis-adjusted shifter linkage, and not engaging the neutral safety switch properly. I would remove all the shift linage, clean lube and re-install then re-adjust everything.