OK, here's the deal:

I have a 1985 GMC Jimmy (fullsize) with 350/700R4 combo. I bought it as a project and therefore don't drive it very often. It has been parked for about 6 months. This weekend I fired it up and went to drive it to get things "lubed up". Well, the tranny decides it doesn't want to work right. I put it in reverse and it slips a lot until finally the truck starts to creep. I throw it back into park, rev the motor a little, back into reverse and she sorta goes. Toss it into drive and start to climb a slight grade in my driveway, I get to the steepest part and the truck just stops, tranny slipping like mad. Again, park, rev the motor, back into drive and she slowly creeps up the driveway. Once I got it on more level ground, I found that it will not shift out of first. If I manually shift it into first, it's like it's in neutral. Shift it in any gear other than drive and it's like being in neutral (except reverse).

This happened the last time I parked it for a while except it was only second gear that "disappeared" on me. Never got that fixed and now I have this problem.

Anyone have any clues as to why parking the damn thing causes the tranny to "lose" gears like this?

The early 700R4's are notorius for having tons of issues. Sounds like the tranny crapped the bed. Does it have enough fluid in it?
I know later on the 700R4's were redesigned and the flaws were fixed, but there not cheap!
If it comes down to it you can always put a TH350 or TH400 behind the 350.

Yup. TH350 for 399 rebuilt out the door.
I just went thought this Ken, I dont envy you bro.
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