I have a 2004 r150 4.6. Trans was slipping a little. We did a flush and fill and I backed out of the shop just fine but when I put it in drive I didn't go anywhere and still can't. Any ideas?

 

Welcome! How many miles on it? Sounds like its time for a rebuild.

 

If it was a long time between the previous fluid change and the truck's at 150-200k it might be replacement time. I've never been a fan of machine flushes. With a very old fluid and worn clutches, there's risk of debris being forced through the valve body from the pressure applied to the system at the out/return cooling lines the machine attaches to. If you have the time and can spare to waste 6-7 quarts of mercon v maybe do a pan dump and refill and see if maybe that clears it out, but if it's not moving, then I agree probably time for a rebuild or salvage yard swap

 

To be fair, that pressure you speak of is no more or less than what the transmission would generate in any other situation. So, if the internals are crumbling to that extent, you’re otherwise spot on, transmission is toast.

 

You just found out why you never do a tranny flush job especially on an old transmission. Time for a rebuild.