Hi, have a 2000 sts with 70k that has displayed "service transmission" readout and code of p0734 "incorrect 4th gear ratio". Car will not shift into 4th gear. Have reset codes and still have same issue. Anyone have an idea what the problem is and an estimate of repair? Is this fixable without going to cad dealer? thanks, Jim

 

There is a TSB for a warped lower channel plate. (01-07-30-005A)
Driving with this condition will damagethe fourth gear band and/or the reverse clutch housing.
If you catch it early it is repairable in the car (drop the pan and remove the lower valve body/channel plate). If the band and drum is excessively worn then the tranny needs to come apart for a proper repair.

I would suggest you have a Caddy dealer do the repair.
If you know someone else who is comfortable repairingthe 4t80 unit then go for it.