So this is a bit of a long story but bare with me.

Little over a month ago I tried to drive through some flood water and ended up getting water in both my Engline via the air intake and my transmission (not sure how it got in the tranny)

In any case I blew the water out of the engine v6 vortec 4.3 by pulling the plugs and turning the key/ replaced plugs and did two oil changes to push the water out (getting ready to do a 3rd) as I added some fuel system cleaner last time.

Replaced gasket/filter on tranny 4l60e and flushed the entire system via cooler lines.
(sadly got black permatex mixed in with the fluid) dropped the pan a 2nd time to replace filter and clean all solenoids after the TCC clogged up and I got locked in 4th (runs like a champ now)

Anyway I've got about a 200yd road leading to my house and this morning I decided to drop into 4wd-high, all worked well until I slowed down and the transmission dropped into first gear then it felt like I was driving with the E-break on so I quickly hit the 2wd button and everything worked fine again.

I've yet to service the transfer case Do I need to drain it separatly from the rest of the transmission ? I've serviced engine/tranny and not sure what other area's are priority though both transfer case and Differentials have been mentioned.

Again the Truck is a 1995 Gmc jimmy with a 4.3 vortec v6 and the automatic 4l60e. "and yes I do realize I am lucky as hell that the water didn't kill the transmission (Previous owner either rebuilt or re-manufactured back in 2008)

 

Sounds more like shifting into 4LO instead of 4HI except if you were turning hard when switching into 4HI.

May need more info on behaviour.