Help with trans problems, 93 Suburban

[Gregory50]

93 Suburban, 4-wheel drive.
Took a trip @ about 300 miles. Smelled sulpher and "service engine soon" light was on. Then @ 5 miles from home transmission slips. No reverse no forward gears worked. Put in 4-wheel drive and went 5 feet until it slipped, as if, in neutral. While waiting for tow truck I started the sub and transmission worked fine for 3 miles then the same occured???
Help Please!! The fluid is full, does not smell burnt but appears milky.

[RexNfx400]

The Transmission filter might be plugged. How it usually goes is like this. The filter plugs from either never being changed or from rapidly failing parts. Why it starts to move again after sitting is because the particles(friction material or metal), fall from the filter into the sump. Then when you start it up, it sucks the particles back into the filter and no move. Shut it off, wait 1/2 hour or so and go again till plugged.
If the fluid is milky(strawberry quick) color then water is in the tranny. Water is very bad for clutch material. Actually, its the steam from the boiling water inside the tranny that kills the clutch material. Clutch material will peel off the steel its bonded too. Best case, change filter and flush tranny and find why water in it. Worse case, rebuild and find why water in it.

One other thing, a bad shift fork in certain transfercases could about have the same symptoms but usually you'll get some harsh noises as it loses and grabs gears.

Good luck...