Transmission Virus

I apologize for this long note but I'll really appreciate your adise.
My '88, 420 SEL, 77K miles, has the dreaded reverse-gear-itis. Reverse has been slow to engage. I changed the ATF and filter and it worked much better, then a couple of days ago I thought I had lost it altogether. I rev the engine and nothing happens for several seconds then it engages and the car shutters as it backs. Previously, before the fluid change, the shift was delayed and if I was parked down hill, it would kick hard into reverse. (All forward gears shift smoothly.) I've searched this form and others. I hope for a miracle fix but the bottom line seems to be a trip to a dealer or transmission shop, and big bucks which I don't have. I read somewhere that the clutch pack can be replaced without removing the transmission. Is this true? I've also read that most dealers and many transmission shops will advise a replacement transmission. But I've also read that some shops will work on the transmssion without tearing it out. Can any one recommend a shop in Dallas, or preferably in northeast Texas (Longview, Tyler, Mt. Pleasant, Sulphuir Springs) that is trustworthy and "reasonable?"