O.K. short version. Have the '00 ecsb Z71, and I have just had the tranny serviced at 120K or so miles. I don't think the tranny had ever been serviced before. Now, before the service I could lock the selector into first and the truck would stay in first no matter how hard or light I was on the gas. Now after the service, same scenario, truck shifts into second if I lift the throttle or if I come close to redline???? What gives????

I did the service for two reasons, one I didn't think it had been done before, and two, I tow a jet boat, 24' toy hauler, and a 30' enclosed trailer with about 10 dirtbikes in it. Not all the time mind you, but on the average the truck sees some sort of tow duty 2 out of 4 weekends a month.

With this being said, I have heard that the newer (99+) Silverado's trannies would do this shifting. I could never get mine to do it. What it would do is if going to fast for first, the tranny would stay in second and then shift down to first on its own. But then it would STAY in first. Now it goes into second and then back down upon slowing?????

Did the service center forget to do something or should I have not done that service, what??? I am confused......help a brotha out, please!!!