Cadillac Repair: Transmission, engine, or what??, cadillac dealer, compressor clutch

Question
I have a 93 Cadillac Deville with 200,000 miles on it.  The transmission started acting funny so I found someone to replace it.  As it turns out, that wasn't the problem.  After consulting my cadillac dealer, the A/C Compressor Clutch had shorted out, causing the ERLS fuse to keep blowing, causing the transmission to act like it was starting in 2nd or 3rd gear.  After unplugging the compressor and replacing the fuse, that problem was eliminated.  However, now its acting funny again.  No matter what the position of the gear shift the car must rev to high RPM's before it begins to move.  (This is not true for reverse, it has great power)  It feels like there isn't much power to the wheels.  So I started revving it up higher to get it to go and it began sputtering and backfiring.  I took it to a local mechanic to run engine diagnostics and he found no trouble codes with the engine or transmission.   The distributor and all the plugs are clean, so thats not the case.  At idle, this car runs perfect.  If revved before you put it into gear, it revs perfect.  However, after putting in drive and giving it alot of gas, it backfires. Then will continue to do that no matter how hard you press the gas after that.  If I turn the engine off, then back on, it runs fine again until revved up high in drive.  I have also replaced the computer and it doesn't help.  Could the transmission be slipping, causing the computer to mess up b/c of the high RPM's required for movement, causing the car to backfire?  I'm about ready to pull all my hair out!

Thanks

Answer
Hi Al, I would check to see what kind of warrenty the trans has and what the installer will do for you as far as diagnosis and repair or replacing this trans. The first thing to do is check the trans fluid and condition. If low or not on the stick then adding fluid might get you going. If it smells burnt or is a brownish color then the trans is probably damaged inside and will need repair. What is the chance you can reinstall the original trans? Where the neg. battery cable connects to the engine block near the starter develops a poor connection. Just looking at it it will look normal but taking it off and cleaning the end and the engine mounting area might cure the back fireing once it is reinstalled and tightened up. BTW all the black paint must be removed from the starter bracket where the bolt and cable make contact. You may have to go to a Caddy tech to help with the diag. because there are other things that need to be checked by a knowledgeable person and can interpret the readings of the car and test equipment. Bill