[Groesbeck Hurricane]

2000 F250, 7.3L diesel, automatic transmission, 250.000 miles, we are the original owners

regular filter and fluid changes, standard maintenance stuff (power steering pump, batteries)

Two weeks ago I replaced the glow plugs, all 8. New main battery, the secondary battery tested OK.

Do not know if this matters, took into dealer for safety recall, they were trying to talk us into trading the truck in, claimed it was leaking oil everywhere. After they had it, it did leak oil and we did have to top up the oil. In changing the glow plugs I discovered two valve cover bolts that were loose on the bottom of each side, the remaining bolts were all at full torque. Miraculously the oil leaks have stopped after replacing the glow plugs. Result: beware that Ford dealer.

This summer we were pulling a heavy load up big hills and the transmission got very hot. Had to replace five quarts of fluid. Did not notice any oil anywhere. Checked the fluid level once a month and did not notice any loss.

Went out and picked up about 7.000 pounds of fence posts from a buddy and pulled them on the flatbed, about 3,500 pounds. Truck did not like going up the big hills but made up highway hills and had no issue at low speeds.

My bad, I did not check transmission fluid after this trip.

This morning the truck pulls trailer out of mud and up a little grade with zero issues. Engine sounds good. I load up the trailer with some hand tools and head out. We have a big hill near the property and I have about 3,500 pounds worth of trailer in back. Truck does not want to pick up speed. Loud and we do not get over 30 mph.

Going downhill we get to 60 without issue.

On level ground the truck does not want to hold a speed faster than 50.

Going up the next hill we drop to 30 and struggle. There is an auto parts store there so I stop and check the transmission and there is zero fluid on the stick.

I go in and buy four quarts, including some Lucas treatment, get in truck and head home. Same issues with hills. Get to my driveway and the truck has zero problem going up the hill in second at 20 mph, no struggle no issue, nothing, just pulls strong!

Add four quarts plus one I had at the house. I have some fluid on the stick but I am NOT convinced the transmission fluid is full. I run back and forth and re-check and have the same amount of fluid on the stick. No fluid apparent under the truck. I hook up the OBD reader and do a test run.

Repeat of exactly the same, zero power, trouble going uphill. No codes.

Return home, check transmission, no fluid on ground or visible under truck, fluid showing on stick.

Disconnect truck and head out in truck. No power going up the hill without anything heavier than me in the truck, cannot get over 40mph. Get to top of hill and turn around and truck picks up speed nicely going downhill. No issue going up the driveway.

Again, there are no codes and everything on the OBD reader shows as normal the entire time.

Any thoughts?