Funny story, but I'm sure you don't see it that way.
I'm sure the back window of a 3 ton is the same one on my 1/2 ton. I managed to put mine in by first using lots of liquid soap. Assuming you've already put in the rubber seal around the window opening, you'll need to pull it back on the bottom and slide the glass in. Then with a flat tool like a thin blade screwdriver pull the rubber away from the edge of the glass as you push it in on the sides. The top corners were the hardest for me but I just took my time and pushed with my thumb and pulled away the rubber at the point I was pushing. It should go as you work it in at the top. Patience was the thing I had to learn. It's just a piece of flat glass, so it really shouldn't be as hard as you describe. I'm beginning to wonder if the hole is out of round and that's what's causing your problems. Make sure you go back and straighten it as good as possible if it's bent.
Good luck.
