I have a 97 Legacy GT, when crusing on the freeway (70-80mph) My tach shows the RPMs reving up and I feel the car loosing power like the transmission is going into neutral. The AT TEMP light and CEL come on and I pull the car off on the side of the freeway and let it sit for awhile 15-30min. and when I start it back up everything is back to normal with no lights. The first instance happend about a month ago , and it has happend twice in the last few days. I have checked AT oil quality and level and everything is normal. When I spoke with my mechanic after it first happend he mentioned it might be a voltage spike of some kind perhaps alternator or voltage regulator related. The thing in common among all three episodes is this only happens on the freeway crusing. Other than a loud knocking noise when the car is cold, i have assumed to be a sticky valve lifter, the car runs fine. She should roll over 100,000 miles in the next couple of months (god willing) and in the expensive year i've owned her i've had to change the HGs, crank seal, waterpump, thermostat, timing belt/tensioner/pulleys, and belts.
I am at a loss for what could be causing this, any ideas???

 

For the first time today the CEL came on when I started the car and the AT TEMP light flashed telling me it has a message. I went and got my ECU code pulled and it was P0753 "Shift SOlenoid A circuit Electrical" I'm going to research it , but i hope it isn't expensive and I don't see how it could cause my AT oil to overheat on the highway just crusing ...