BMW Repair: Transmission ?, high mileage, likelyhood

Question
3 months ago we started a restoration on my 1984 318i, we raised the rear pretty high for body work the next morning we found a puddle of transmission fluid. I kept this in mind and after another 2 months we finished the restoration. I remembered about the transmission fluid so before using the car I checked the level and it was normal to my surprise. On the third day of using the car I ran fine for about 4 miles and then I lose power. The car would not go past 25mph on a upgrade with the pedal to the floor and on more level grade up to 35/40 but kept sliping out of gear. Again I check the transmission oil and again it was normal. Any ideas on the problem. This car has had a complete overhaul on the engine but the tranny is original with 300,000 miles on it. Never had a problem before and the oil is clean. The transmission is automatic and I believe a Z22.

Answer
Dennis,
 300k on an automatic that has never been rebuilt is astounding.  I'm suprised when I see automatics lasting to 200k!  Its very possible that the transmission is just shot.  Its got extremely high mileage for an automatic, especially one that hasn't been rebuilt.  You can change the fluid in it and it might help, but in all likelyhood... it's just worn out.
 The best thing to do is to take it to a tranny shop and tell them exactly what you told me, they will probably know exactly what the problem is.

 Good luck,
 Josh