Does trans fluid wear out

To answer the question of does fluid lose its viscosity. As soon as any fluid is in any vehicle it starts breaking down. The only time it is 100 % is when it is installed. It's all down hill from there. Now can this cause your problem ?? Maybe. There are also numerous other things that can be causing your symptoms. A trans fush ( and make sure they are using a quality flush product that actually suspends the partiiculates and flushes them. Not something that just loosens the junk up) I recommend a Valvoline flush treatment and new filters. If done properly you wont have any problems, but dont hold me to that. We do proper flushes on lots of high mileage transmissions and have not had any problems with the proper equipment and fluids. (knock on wood). Electrically it can be the PCM (powertrain control module) or the TCM (trans control module) or sensors as well. Lots to look at and diag. The worse being the trans is just tired out. Prob didnt answer any thing for ya, but maybe something will ding.
Good luck

-RPM