Rear diff trouble

Just wondering. What have you done to rule out something simple like bad U-joints?

If this were my car I would also be looking at the slip yoke. As well as all of the suspension points that might allow the axle to rotate the pinion up/down.

If it does turn out to be a problem inside the rear end itself almost anything wrong with a rear end (short of major breakage) can be repaired with a rebuild kit. The Ford rear end is a very "serviceable" unit.

I also thought the the transmission controller would not let an automatic go into reverse while going forward.

Have you considered the GF 2.0 upgrade?

the GF 2.0 would definitely be your most cost effective way to go lmao

but I second starting at the simplest solution and working up from there. However if you haven't serviced your diff a fluid change can do wonders..... however not if you need a rebuild because then you would be doing the fluids anyways

so now is the wonderful internal debate to get a rebuild kit, or if your taking them out then now would be a good time to change your gear ratio if you were thinking about it