With tthe assistance of my brother, I replaced all of the old fluid in the transmission by using the fluid ereturn line as the drain.

There is a sticky detailing how to do it. Because my truck has the dipstick (2003 4speed) , I had my brother start the rngine, and the fluid would pump itself out of the return line into a pan, about 4 quarts each time. I would dump the fluid into a gallon container (old windshield washer bottle) that I had already marked with marker showing quart levels. This way, I knew exactly how much to put back in each time.

After I reached the 13th quart , fresh fluid was starting to come out. So I refilled to the cold mark on the dipstick, and drove around until it was warmed up (about 1/2 hour) . Checked the fluid level, it was down about a quart, and filled.

It's been fine and does shift just slightly smoother. I will say the old fluid did NOT look all bad. It still had some red color to it and smelled just like the new stuff. No burnt smell. I don't know how long a transmission would last without the fluid change, but it must depend on how hard it's used. If the truck is a daily driver with no towing or hard wheeling, it probably would last a long time like Toyota says. BUT it's easy enough to change out and have that insurance that fluid problems won't be an issue.