i have had my 47re trans do similar to that and, I took it to the dealer and had the computer re flashed and that solved the problem. it would shift in and out in OD
at 45 to 65 for no reason. just another option to look at.

 

If you have oversized tires the computer is trying to compensate. Mine and my buddy's 99 did the same thing when we went up in size. Go to a shop and have them put the new size in the computer it should help.