Chrysler Repair: Gas mileage/Speedo error after trans repair, speedometer accuracy, drb iii

Question
Hi Roland, I have a 1997  Chrysler  T&C LXI 3.8 Extended .I recently had the trans supposedly rebuilt .I suspect He put an older junker in it .My gas milieage has fallen by 1/3rd . I was getting 27 to 29 on the road , now I get 20 to 22 at best .
today I found out that My speed is about 57 when it says 50 .what do I need to do to restore My true readings ?

Answer
Hi Dan,
There is a progammable factor in the transmission control module that is adjusted to match the distance travelled as shown on the odometer to the actual distance travelled. It is called the pinion factor and so if a transmission with a different overall gear ratio from what was in the van originally was installed then the pinion factor has to be reset to make the proper match. This apparent discrepency suggests that you were sold a different used transmission rather than repairing the old one. Repairing the trans does not change its pinion factor.
A professional level diagnostic readout box such as the Chrysler DRB III which can communicate to the module is needed to make the adjustment. So I would begin by comparing the odometer reading against a measured mile, such as along a highway where either there is a "speedometer accuracy check" area or which has mileage markers posted. Then once you know how far off you are you can have the shop with the necessary readout box change the pinion factor. Or confront the shop that did the rebuild with the evidence that your trans was not actually rebuilt.  
I would believe that factor error correction will reduce to some extent the apparent loss of gas mileage because of the fact that the speedo is reading low which also means the odo is reading low. You could also at the same time that the shop is doing the pinion factor reset also have them readout the trans control module for any error codes that might reveal either a shoddy rebuild or faulty substitution. These would be 4-digit code numbers prefixed with a P. Ask for the numbers, what they mean, and what should be done to correct; then write back and we'll compare noted with the shop manual for the same code.
Roland