I have a 1995 E320 automatic with 116k miles. The car has worked great until yesterday, when I noticed a funny little rev in rpms on the freeway. The car did not lose power, and then went back to normal, and I actually wondered if I had imagined something. This morning it started fine (low 30 degree outside temps), and ran errands. Parked it, and 30 minutes later tried to leave and the car started normally, no unusual sounds, idled fine, but the car was very very slow to transition forward (speeds of 10-20 mph). The rpms would wind up to the 3/4,000s and I would back off and it would eventually "catch" and move forward after approx 5 seconds. I checked the ATF, it was a little low, so I added 1/2 quart. The car idle is now between 500-1k. The car continues to do the same thing even when it has warmed up. Once it gets up over 25mph it seems to run fine, and reverse has remained fine, 2nd gear fine. 3rd gear and drive seem to be the issue. I spoke with a mechanic who said that if it wasn't the ATF, the transmission would need to be rebuilt. That seems like a big leap without looking at the car, and when I asked if it could be something else like the vac modulator he said no. Do transmission problems start this acutely? I am really hoping this could be something other than needing to overhaul the transmission, any thoughts? I can't get into a mechanic for a couple days and other than driving it around the block a few times, I assume it is best to let it sit till then. ANy thoughts, ideas would be really appreciated!! ATF fluid is red, and looks clean.