Expecting to have to replace the full transmission, my mechanic determined that it was actually the transmission's pressure hose that needed to be replaced...
After realizing it wasn't the entire tranny that had gone bad, they shifted attention toward the actual pressure control unit ($1,400 part)... luckily it was just the hose. After also fixing a radiator leak, the whole bill was just under $1,100... a bargain considering the alternative.
I was going to have to sell my Fender American Telecaster to pay for it all... glad none of that happened.
Make sure you have a knowledgeable, trustworthy mechanic!!
Got her back today and is running well.