Subaru transmission quandary

[jonpolk]

I have a 2000 Legacy GT Limited with 100k miles. It is an automatic and shifts very hard between 1 and 2nd. The AT Oil Temp light occasionally comes on. I took it to an excellent, experienced, transmission guy who I have used before on other cars. He partially took it apart and told me that the transmission was fine, the problem was up the line somewhere, something is sending faulty signals to the transmission. He told me to take it to the dealer to have them hook it up to their diagnostics, but warned me they would probably tell me to replace the transmission, and because they would replace everything up and down the line along with the transmission, the problem would get fixed, even though I didn’t need a new transmission. The dealer wants to put in a new transmission for $4,500. The transmission guy says the transmissions is still good, but would charge $2,500 and is sure that changing it will not fix the problem. The car is only worth $6,500. I hate to spend the $4,500 when it is not necessary, it is just no one has been able to diagnose the exact problem. Any help or ideas would be greatly appreciated!