[Tin Injun Tom]

I need an opinion from an auto/trans pro as soon as possible.
94 Grand Prix with a 3.4 litre. The trans abruptly "goes nuetral" as you're accelerating through the gears. Started out doing it on gear changes. Not every time, but mostly when getting on the throttle moderately. Only for a second or two, then it drops back into gear.
A day or two later, and it now seems to be quite worse. Even when babying the throttle, does the "slipping gear shift" thing almost constantly.
Not only that, Going along at 30 mph with rock steady preasure on the gas pedal, the revs just arbitrarely jump up 500 for a half second or so, then the tranny continues to pull.
The latter makes me believe the clutches are not slipping. Does this sound like a weak pump? or perhaps the screen is clogged, ie starving the pump for fluid. I hate to drain the pan if it's not going to do any good.
Fluid level is full. Car has 199K miles But don't know if the trans has ever been replaced. No way the car is worth raplacing the trans. Just want to see if we can eek out a few thousand more miles.
Thanks for any help.