I have to chime in on this one;
The MLPS, which is also known as the Neutral Safety Switch, and the Transmission Range sensor, is usually the culprit in the case of the Tranny "suddenly popping out of gear".
The 94's had a poor gasket design, which has since been improved.
You can replace this part yourself, in 20 minutes, at a cost of under $65.
If anyone tells you that you need a rebuild, based soley on this problem, I would run from them as fast as I can.
My 95 LX 4.6 4r70w has 190,000 miles on it, and it is all original. Read the Tech Articles on the transmission over at
www.tccoa.com, and you will see how awesome these trannies can be.