Hello. We are having a problem with our 2006 Chevy Silverado 1500 HD with the towing package. It is the 6 liter motor and the 4L80E transmission. We hope you can help us figure it out. We have a separate radiator for the transmission. The transmission is heating up to about 195 and when it does it shifts really hard in all the gears. When it is cool, it shifts perfect. We thought the "hard shifting" was the U joints or/and the center bearing. Upon inspection the U joints were good but the center bearing needed replacing. That did not solve the problem. We can do most of the work ourselves but run into trouble when we can't pinpoint the issue. We are hoping you have a list of common problems for this specific issue and for this truck. Thanks so much!