As of recently my parents have had a lot of problems with their Chevy Venture van. Sometimes we will be driving along and the ABS light will come on and then it feels like the transmission is stuck in 3rd gear. We've figured out through some trail and error that the problem is being caused by the voltage surging the car (15-17 volts.... We measured it on a volt meter). So now we've taken it to a shop and they have replaced the alternator and the brain and tried a few things with the wires, but the vehicle still has the problem. We've observed that it happens more when it is hot outside (100+) and it generally happens when you are slowing down (Like going to get off the highway). A couple of times it has done it right off that bat out of the driveway, but our driveway is a little steep too. Does any have any suggestions of what might be causing the problem?