95 Buick LeSabre Transmission Problem

Hi all. After taking car into dealership to diagnose slipping,hesitation problem. I told them it might be a transmission problem. They charged me $322 to change the fuel filter, replace a wire that had frayed and sent me on my way. Three days later, the transmission failed as car would not shift out of 1st gear and 2nd gear and no reverse. Anyhoo, now they want to charge me $550 just to diagnose the problem, which could run up to an additional $3500 according to the "Service" advisor. I asked the guy what tests they performed and he couldn't tell me.

Shouldn't he at least run a diagnostic to check if a solenoid was working or some sort of torque converter inspection/test, or what about the EGR valve? I can easily envision this dealer charging me $4500 for a $200 repair. The courtesy driver (8 year employee), with whom I have become very acquainted with as a result of my many, many return trips, has told me that their service business has been slow as has their car sales, and the general manager of many years has recently quit.

My questions, gentle readers, are these:

Can anyone recommend a reputable transmission repair shop in the DFW area as I have lost all trust in this dealership?
What questions and specific diagnostic reports should I ask to see to justify an enormous expense?
Is there something that I can check myself prior to taking to another shop? I don't mind crawling underneath and getting filthy dirty. :)

You can check a couple of things. Oil level with the vehicle running, in Park and transmission at operationg temperature. Smell the oil to determine if it is burnt. Take a couple of drops from the dip stick and rub it in your fingers, it should be clean, if it leaves a blackish film on your fingers there are metal particles floating in the transmission, not a good sign.
If no one recommends a tranny shop, go to a few of them and get free quotes on the tranny. The main thing here is to see if you get the same story more than once from the different shops.

For what it could feasibly cost to repair the transmission, you might want to look into buying another car. Or a different transmission, refurbished or lightly used out of a junked car. You'll probably save yourself money.

Just so you know, don't buy any transmission used if the fluid is brown, if it smells like burnt rubber, or if you see miniscule flakes of metal in the fluid in direct sunlight. If you go to the junk, find out why that car is there in the first place. Sometimes you can find a car that is the same as yours that has a motor problem. It might be cheaper to buy that one and swap the tranny (if it doesn't have any of the indications shown above). That, and you will have a priceless slew of parts at your disposal.

Thank you gentlemen. I appreciate your assistance.