I am not sure if this guy was telling the truth or not, but when my reverse in the transmission in this truck went out at 700 miles, I was talking to the service writer about it. He had mentioned that that he had worked in the transmission industry the prior 17 years. He said for the most part a transmission flush was a gimmick to sell the customers a higher priced service. The only time it should be done would be if the transmission had seen a lot of miles without a change in fliud and filter. He said it was a gimmick because most times the flushes aren't done properly and if they are done right they are expensive.
He said the right way to do it would be to drop the pan and put in a new filter and then flush. No sense to flush good fluid through a dirty filter. Then drop pan again and replace filter again with a new one. Now you can reflush and top transmission off.
He said really the best way is to just drop the pan and change the filter every year or 15,000 miles. As long as the fluid is red its still in good condition. I'm not sure how much he said was true and just passing it along in case other have heard similar statements and might be able to validate them.
He mentioned the obvious of making sure you are towing in the proper gear and not in O/D, unless the RPM's are up, because lugging the engine and making that transmission heat up will speed up the death cycle.