Don't mix, I went threw a hole the other day at Big Boy's playground trying to show up the Chevy boys ( which Stampede did over and over again even pulled a few out) goin threw the hole in 2wd a lil too fast and got too much mud and water in the engine compartment. I took the alternator off today (finally got decent weather, man I'm sick of the cold) and when I spun it by hand I could feel the mud and grit in it. Anyhow $129 to the local Advanced Auto and a lifetime warranty. So an easy fix and my trans pump seal isn't leaking anymore. I read on other posts when I did a search here on FTE that it is a common problem with the E4OD when the temp gets on the hot side so, I'm going to mount an electric fan so when I am wheelin and not having a lot of airflow threw the cooler the fan might help. I'm going to replace the pump seal anyhow, others have said the aftermarket seals withstand the heat better without leaking. My biggest concern was keeping the trans cool since I know that extreme heat will eventually kill it. With 170,000 plus on the odometer everything works great. It will continue crush "Rocks" and $#!T Rams and when it she's ready to give up the ghost I've got 2 460s and a C6 in the garage just beggin to be put into something. Can you say 545? And Gary the boys got the motor outta the rollback today so I'll be able to get down there tomorrow and make room for your truck.
Have you checked on parts for rebuilding the alternators? Take it apart and give it a good cleaning with WD40 get a rebuild kit at the local parts place and have a spare. I can't remember how much they were but it would be alot cheaper than $129. I know there was a rebuild kit for my 88 F150.