Thanks to holyrider and TheCrazyFarmer I have a T98 in my garage. I plan to tear it down and rebuild it over the winter and will document it here. Transmissions are a mystery to me, but this only cost $25 so its OK if I screw it up or can't get it back together. Hopefully the process will help me figure out how these things work a little better. It reportedly popped out of third gear under load nearly every time. I don't know if it's related, but I noticed that the input shaft/main drive gear has a lot of play in it compared to the transmission in my own truck.