Park Avenue Ultra 1994.

I get confused, some sources say 4T60E, others 4T65E, others 4T60E-HD, others 4T65E-HD.

Am I right in assuming that the 4T65 came later, in 1997 or so? And that all Ultras have the HD (heavy duty) model while the regular PA has the non-HD? Can I identify my tranny visually somehow? Serial number?

Thing is that I get the no-4th-gear problem and it seems like I might want to swap the TCC (?) solenoid.

Local auto tranny specialists helpfully suggest fixing my tranny will cost about $3500. They can go kiss, and I would like to find and buy the proper solenoids for my tranny and hand it over to some generic barn mechanic instead.

Any help would be highly valued.