Hydra-matic not shifting past 2nd

I was having some unrelated work done to my 62 Cad Superior and he had the car for about a month.
When I went to drive it home, it would not shift from second to third. First and second seem fine, but I cannot get it upshift beyond that.

It is a jetaway so there is no vacuum

Check for a low fluid situation. Cars don't like sitting unused, and the seals start to leak. Good chance it is just low on fluid, or the front coupling has a bad seal, or is damaged. The last thing that I can think of is to try a bottle of Red Lube Guard with the transmission oil. The one that you want to use is UPC 83137 60902 (I have a bottle is sitting on my computer desk). I have also had good luck using Trans Tune Transmission Treatment by Sea Foam. I used that in the Chevy when the transmission wasn't shifting properly on the way home from Iowa, it cleared up the problem, and has been fine ever since. That car also sat for a long time without being driven, until I purchased it.

they tell me the jetaway will do that. one guy said all you need to do it ker-cunk it. shift it from forward to reverse and back a couple times and it will pop the band loose. it sticks when left to sit a long time.

Replaced filter?

My '64 has the same tranny I think...with the (R)everse all the way to the right? I was having some issues with it and after a couple of transmission shops recommended a complete overhaul--a last stop at a older gentlemen's small shop said to replace the transmission filter first before a rebuild. I did that and it corrected the problem.