Like the title says, but I know there are a few GM mechanics out there. I have a few questions pertaining to the trans in my GMC sierra. It has the 4L60E trans. When driving down the road at 60-65 mph in it feel like I loose all power and then it will thump back in gear. Its not slipping or gradually losing power, it's all of a sudden. It has not been doing this long and is very infrequent. Also it only happens when it kicks on up in to OD. I like to old truck and don't want to send it to the junkyard in the sky if I don't have to.