Help request from a newbie: Zero Reverse '00 F250 7.3l 3.73

[Groesbeck]

I have done a search of my symptoms and came up with some answers but not everything I was hoping for. I missed something somewhere...

Background:

Owned truck since new. ~225,000 miles, 2000 F250, 7.3L, 3.73 rear end, 4-spd auto, zero modifications.

Truck is super-duty XLT with complete towing package and beefed up springs for hauling. about 1/2 of life is spent towing from 3,000 to 12,000 pounds. Normal maintenance pulled (oil, filters, tyres, batteries, speed sensors (often...)). Only outside of above is new water pump, new A/C cooler, and brakes/shocks. Truck does NOT have PTO option.

Recent:

Just completed ~1200 mile round trip empty one way, returned with 20 posts with a weight of less than 1000 pounds. Average of 18 MPG on the highway for the entire trip, normal.

Symptoms:

There are ZERO codes being given by the truck, nothing.

About two months ago the gear selector on the column became loose. Sometimes it does not fully seat in Park. On occasion must put selector in Neutral to start truck.

Day after trip, attempted to move truck and truck will not go in reverse. We can apply fuel and the tyres do not move. We can drive forward, went through three forward gears. Some noise from under and I believe in the back/differential but this is more of an impression and could be wrong. Truck did finally back up some but there was a clunk and it stopped moving backwards.

Fluid is full and does not appear discoloured or burned.

Truck has ALWAYS had issue going up grade (with or without load) when the road surface is loose. Does not matter the type of tire used, do not know if this even matters...

Attempted Diagnosis:

Does this fit into the realm of the torque converter? Transmission has never given issues and has had no repairs. Differential has never given issue either. Motor starts and runs fine.

Actions:

checking codes (none), checking fluids (appear OK), resetting by removing batteries (no improvement).

Input:

Requesting any input from the board! Thank you!!!

[Zander's 5.8]

Do the RPM's go up alot, like the trans is slipping? Or do they go up, and stay at a certain RPM like it's struggling to move? If it's the second one, pull the rear brakes apart. It's common for the parking brake shoes inside the rear rotors to come apart and get jammed up when trying to drive in reverse.