Till one morning you find that it takes a little longer to shift out of the 1st.
Then you think you'll just change the fluid a couple of times and it'll go away like it did the last time.
And it doesn't.
Then it takes a fully city block to shift out of the 1st.
Then it takes a mile to shift out of the 1st, but it happens in the desert, so you don't care.
Then you pull the Y-pipe and transmission pan and change the filter, too.
It still does it.
Then you realize that you need to replace some obscure parts in the transmission oil pump, and need to pull off the exhaust, driveshafts, and transfer case.
You find that the parts are few and far between, and shops willing to work on these transmissions are nearly inexistent.
You still find the obscure parts and do the job yourself or farm it out to an indy shop you trust.
Pay your bill, take the keys, and drive the truck trying to convince yourself that it is fixed. It isn't.
This kind of robust.