Hi all....I'm new to this so pls have some patience...

I'm in the process of putting a 2000 A4 2.8 AT on the road but running into a "limp mode" problem.
At first it was intermittent but now I have only the one gear.
For those of you who have solved this problem, I have great respect !!!
I'm not sure if its 3rd or 4th gear that I have but I'm trying to figure out what it could be.
I don't believe it's the transmission because that would be a catastrophic failure, not a partial or intermittent "limp mode failure" that is now steady state.
I looked at the TCM and while there was some condensation on the interior of the plastic box/holder, none of the terminals had any oxidation on them.
I opened up the aluminum enclosure but did not see anything out of the norm.
Mechanic told me to bring it inside and dry it out. The car was sitting for three years but initially, Was completely functional.
I've read many posts on this and I'm thinking its a hose, tube, or something "simple"
Can anyone offer any preliminary checks or inspections before I pay good money to have the car diagnosed by a prima donna ?

 

any codes?