Originally Posted by
Nathan Turner
I have a 2015.5 lml, started having the same issue with it. Iv done quite a bit of research with Allison and GM.It has a T87 tcm witch Chevrolet decided to take over the electronics side of Allison in 2015. Turns out GM started putting there on valve body on witch has a spacer and gasket between the valve body, it has twice as many holes in it to release the line pressure faster takes away the hard Allison shift, that we who pull know is needed to keep the trans from slipping. My builder is working with GM now to try and come up with a solution for my issue.