Noises During Shifting problems of the 2004 Toyota RAV4

I drove my 2004 (6 1/2 year old) Rav4 sport awd today as usual to work (16 miles). It has just short of 50,000 miles on it and is ready for the next oil change in more than 1000 miles. I have done the majority of maintenance at the dealership. I drove the car from my office at 169 and 62, on 62 then north on i35w to minneapolis and then on i94e to st. Paul. Soon after I got on i94 I noticed sudden failure to accelerate with a jerking and high revs (to about 4500) when going from 55 to 60. The gears did not fully engage and rumbled and did not change or drive fully in any gear. I was concerned about transmission problems and stopped at a service station (mike's bp in st. Paul downtown) that had done an oil change on my car. The service person checked my transmission fluid and said it was "filthy" but full. He said it may need a new transmission. I chose to cancel my trip out of state for work, and drove directly home after setting up with my regular mechanic for next Tuesday, the earliest open appointment. I was surprised to have this issue come up so suddenly and it is a clear danger since I mostly would drive on interstate highways in rush hour traffic or long distance for work and it could cause a crash. I will not drive the vehicle. This car had no issues at all so far - only replaced the wipers a year ago. I am concerned to have further damage to the transmission as the car drove so unpredictably and makes strange noises now if it is shifting. I have a Toyota purchased extended warranty good until end of June 2011 and I'll work on getting this covered. It is frightening to have this happen to my vehicle as I depend on my car for work trips and for commuting. I'm glad I have the warranty and will have the work done to fix the problem if that is possible. My car goes through regular maintenance at a Toyota dealership and they run checks for any recalls every time it is in the shop. There has been nothing at all on the vehicle thus far.