1997 GV 3.3L automatic shifting troubles

[threespeed]

Help!! I replaced my battery Saturday in my son's van because the guy at Autozone said it was bad but the alt. was charging fine. Tuesday afternoon the the battery light came on and the van died at a stop sign. I jumped it off and went to autozone again they charged the battery and checked it and said it was bad they replaced it again. this time when we started the van the battery light came on while the guy was hooking up to test the alt. He said it was not charging. I removed the alt.that night and took the alt. to autozone to be tested. It tested good two times. I decided to replace it any way because of the pain in the a$$ that it was to remove. My son and I put the alt. on last night and he drove it around the block. All was fine. Today he left in it and came back a few minutes later saying the van was shifting very erratic. I drove it and sure enough when it shifts from 2nd to 3rd the rpm's shoot way up and it may or may not shift. Could this have anything to do with the alt. change? The van has 230,000 miles on it and this was the first alt. it has had. Also the transmission was rebuilt a couple of years ago. The battery light has not come back on.

[RIP]

Sounds electrical rather than mechanical. Also sounds like the transmission has detected a failure and has gone into what is called "limp mode" meaning the transmission does it's best to stay in second gear to prevent excessive speed, therefore more damage. Are you seeing a service engine light? The OBDII fault detection system will store a fault code and light the light indicating a problem...in most cases. Some faults will not make the light come on. Recommend you do the "key dance" to check for codes. Better yet, go to Autozone and have them read the codes with a scanner. It's free and more thorough. You may have to visit your dealership or a shop to get even more specific transmission codes.

Why has this happened? "Clean" electrical power is essential to TCM and sensor function. Just a theory but, in the process of breaking electrical connections at the alternator/battery you may have created a spike that effected the TCM or one of the sensors it uses or a sensor and/or it's circuit may have been physically damaged in the process.