Transmission Problem

[z71chevy1996]

I own a 2002 2500HD, Crew Cab, 8.1L allision transmission, with 105,000 miles. I have owned it since new and have had nothing but good things to say about it. Last year while slowing down the transmission would lurch and you could feel a thump as it was down shifting. After i took it the shop to get the power steering fixed because I couldn't move the steering wheel when you where stopped on a hill in either direction. They replaced the hydraulic brake booster and this kind of fixed the problem, at least I could move the wheel but I still had to move it in quarter turn and not all at once. I told them about the transmission problem then and they reset transmission computer and changed the filters and fluid. This fixed the problem for about a year, but six months of that I was deployed overseas, and have only been driving it since July, and now it is doing it again. The previous time it only did it with the A/C on and when it was cooler outside. Now it does it on all cases. Any ideas. I am about to move to Alaska in three weeks and don't want the truck to die going up there, especially since I will be hauling a car hauler and 65 Chevy truck almost 4500 miles through Canada and Alaska.