Bought my 03 with 95k miles or so. Unknown service history. Had the transmission drained, fliter, and filled. Did a bunch of miles and then a drain, filter, and fill. That was about 30k miles ago and zero transmission issues. The first drain was pretty dark looking fluid, seemed really old and maybe original. Second drain was much better looking fluid.

Recently did a drain, filter, and fill again while changing the diff fluids and swapping the center diff out. Transmission shifts great.

 

@mnl01, I did the flush ghetto style: Drain fluid, refill with transmission fluid, drive around the block, drain, replace filter, refill. Of course, that is not a full flush, but you get more of the old fluid out than with just a single refill. I strongly assume this was the first transmission service for that vehicle at about 100k miles. No difference before and after, so I assume that this procedure is safe.

@SeaRover, when you can crawl under your truck, you can do it without rack or jacks. I do it this way and I have no lift, just stock suspension and stock wheels.

 

My fat @ss would get stuck under my Disco if it wasn't for my 2" lift. lol