Transmission Broken?

I have a Lumina from 97, 3.1Liters, automatic that has a transsimission problem. What happend:i was driving it with 75 miles/hour on highway.I started to lose speed and i pull on the right side. Under the engine i nottice that are oil drippings. I call the towing company and taket to the first shop, not knoing what is the problem, The mecanic told me that is the transmission,:banghead: and it will cost me 2k to fix it. the fluid was black in stead of red how usualy should be. I added fluid and drived home for 110 miles , and i bring it to a shop where they change all the fluid, and i get the same answer. :banghead: . i need a different oppinion and i went to Amcco to be tested on the computer. The guy told me that is the transmission again and it will charge me 2800$:2cents: to fix it:banghead: . after the mecanic change all the oil still has a leak of oil but not that much. the mecanic change also the oil filter for the transmission. and still is leaking . Since like a month ago i had to put just like half of quarter of oil.Every time when i start the car she needs less than 1 minute to "warm up" and after that runs great on the road with no problem. In that minute that she need to "warm up"i am able tho shift all the gears , and if i push the acceleation pedal it moves very very slow, and i prefer to wait and do nothing. Can somebody help me? It is the transmission ??
Thank U

This sounds like a valve body problem. Where is it leaking from? Running it low on oil, will for sure cause problems. You ned to get the leak looked after first in my opinion. From there I would be looking very closly at the valve body of the transmission. There are also thermostatic elements in these transmissions (4t60e)that, if they are not working properly will cause all sorts of problem too. The forward servo thermo element is one that can cause a problem similar to what you describe. Either way, you need to fix the leak, and go from there.