Chrysler Repair: transmission: gear ratio errors, chrysler town and country, speed sensors

Question
Just put a 1999 Chrysler transmission into my 1997 Chrysler town and country. Changed the speed sensors both input and out put. The car drives fine at first , then after awhile it reves into neutral and will not shift , occasionally it will catch and then back to neutral.
Does the computer have to be reflashed?  The error code I get are gear ratio 2 incorrect, gear ratio 4 incorrect.

Answer
Hi Gerard,
Gear ratio errors are typically associated with problems with the internal clutches. Was this a used transmission or a rebuilt one?
There is a learning period shortly after a change out of the transmission or the trans control module. You can try doing some repeated accelerations from 0 to 50 at a moderate throttle opening to see if the 'learn' will cause improvement.  I an not knowledgeable about reflashing issues, but if the transmission has the same model number as the old then it is probably not materially different.  I will see what else could be the cause and let you know by a revised answer.
Roland