Transmission Solenoid Problems of Mitsubishi Lancer

I purchased my vehicle in 2009 from the Mitsubishi dealership in GA, brand new. I travel often and long distances so I have accumulated a lot of mileage on my vehicle within a short period of time. I maintain the vehicle with all the proper inspections and services and the suggestion times (oil change every 3k miles, brakes and tires at 50k,. . . ). I began having issues with my transmission in August 2012 with this whining noise everytime I accelerated. My "service engine soon" light came on shortly after the noise started. When I took the car to auto zone, they pulled a "failed shift solenoid" code. I had a transmission fluid flush done at around 70k miles with the proper cvt transmission fluid added to the vehicle. When I was traveling the highway for christmas from missouri to georgia, about halfway through the trip I saw this red signal on the dashboard that read "slow down!" with a thermostat above the warning. I read through the manual and google searched the warning and read that it meant that the transmission fluid was overheating. For the rest of the 13-hour drive, anytime I drove over 75 miles an hour for more than 30 minutes the light would come on. I tried to ignore it at one point and this caused my transmission to stop shifting (I have an automatic). I had to stop 4 times between the trip because of this light. I have a power-train warranty on my vehicle for 10 years/100k miles. While in savannah, I had the Mitsubishi dealer run a diagnostic in which the service technician indicated there was an internal transmission issue. They were unable to resolve the issue at the time because the dealership was closing. Now back in missouri, the dealership is "unable to replicate the code" and is more bent on making me pay the diagnostic fee. Mitsubishi customer care isn't much help either. I feel like I'm going to be stuck on the side of the road soon. Somebody help!.

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