2000 Toyota 4Runner 2000 4 Runner OBD code P0770

I am having a hard time getting re-inspected due to a P0770 code showing up even after the toy dealer has had the vehicle several times. Last time the dealer did a power flush and told me that that corrected the "solenoid" problem, well guess what the check engine light just went on again. Funny thing is that the truck runs and shifts great, just like when it was new and the dealer is telling me I need a new trans ! Has anyone ever experienced this before, how hard is it to replace these solenoids?