Look at this another way. While you're jogging, you are breathing heavy and sweating. When you stop, you really start to sweat more and feel hotter than blazes. Why? No air blowing across your body--not moving. So your truck is doing the exact same thing. While moving, it's at 1 temp, you stop, and temp climbs. Like others have said, use 4 low. You should have synthetic oil in trans, if not switch to it. I wouldn't worry about 225* as long as it was short in duration. If running down the road and it's at that temp, then I'd start to get concerned.