99 f250 auto trans not staying in overdrive
I have a 99 f250 diesel 4x4 with auto transmission and 220,000 miles. When going up a hill even a small one when you push on the gas to get on over the hill the truck quickly shifts out of overdrive. It has plenty of power to pull the hill just kicks down to easily. I have had the trans rebuilt twice and both times it worked better for a while then goes back to doing the same thing. At work we have the exact identical truck and it holds in overdrive much better on a hill than my truck. Is there any thing I can do to get it to work better?