Allison shifting

[Montana Sky]

The parking pall on the Allison is tested to hold more than 22,000 lbs against it. While setting the parking brake under a load is recommended, I do not understand how parking on a slight incline would create enough resistance that one would have to set the parking brake before shifting the truck into park? I remember a time on the boat ramp while loading the boat, I had shifted the truck into park and forgot to set the parking brake. After getting the boat (a 29' cruiser) secured to the trailer, the truck shifted out of park with little to no resistance. This with more than 10,000 lbs pulling against the truck/transmission on a steep boat ramp. It is my opinion, but I would have your transmission looked at as something does not seeem right.

[8.1al]

If on an incline I set the parking brake or it will be hard to get out of park. That's just the way it is, no big deal, it's not the first transmission I have had like that.
A few years ago I asked an Allison dealer about doing some work on our wayyyy out of warranty Allison and was told that they were not allowed to work on them, I would have to go to a GM dealer