truck trans quit?

[Grumpy]

Hey everyone! I just bought a 93 k1500 with a th400. The guy I bought it from said a few weeks earlier he was driving home and completely lost 3rd then 2nd then 1st, and he said it ran completely fine right up to the point of losing all the gears. Does anyone have any ideas of what could if caused this?

http://garage.grumpysperformance.com/index.php?threads/th400-rebuild-turbo400.508/

are you low on trans fluid or is there any indication it leaks fluid?
is your vacuum line to the modulator valve connected to vacuum?
is there any trans fluid in the modulator valve vacuum line?
with the truck up on jack stands can you turn the rear wheels with the drive shaft when the trans is in neutral? does it lock up in gear?
can you start and run the engine currently?
have you put the truck up on jack-stands and verified the flex plate and converter are bolted together and undamaged?

have you pulled the oil pan on the trans to look for mechanical debris?

lots of pictures and more details will help the diagnoses