Having an overdrive solenoid problem

I have an overdrive solenoid issue. After going into limp mode Friday about 4:30 pm I took it to my regular mechanic where he performed a diagnostic reading that returned the code PO760. After a little research he found it was the overdrive solenoid and referred me to a transmission shop. (Note the amount of transmission shops in town are limited, and although he had never done business with this particular one he had heard good things about them) my mechanic then cleared the code and I was able to drive home. This was about 5:00 pm Friday before July 4th so all shops would be closed till Tuesday. The truck drove home perfect (which is about a thirty minute drive) and again back to the transmission shop with no issues. The mechanic at the transmission shop suggested I wait to see if it does it again or if it was a fluke occurrence. After leaving I was almost home when the check engine light came on and it went into limp mode. I was very close to the house and there are no shoulders on our county roads so I decided to "limp it home". I had a wrecker come out and tow it back to the transmission shop. After talking with the mechanic I was pretty much given two options. He said he would drop the pan tomorrow and check for any junk and debris. Based on what he finds he will either recommend a new solenoid pack or replace the transmission entirely. His position is that it would be pointless to replace the solenoid if there is garbage in the transmission because it would only contaminate it, and it would only be a matter of time before it went out again. My question is does he know what he's talking about or is it a bunch of bull? He seems like an honest man, and my mechanic and a close friend who was also a mechanic before he retired both have good things to say about him though only from word of mouth. Any help would be great. I just do not want to be taken advantage of. I have also been warned that transmission shops push for replacing the transmission entirely when sometimes it is unnecessary. Thank you!