Hi, I haven't built to many c6 trannys, and I have one for a friend that just kicked my butt. The only history I know is he had someone put a B&M shift kit in it and it was now shifting softer than stock. So he brought it to me and I freshened it up as well as put a sonnax servo in it and change the lever to a more agressive ratio. Now the issues, the trans will shift by itself freewheeling on stand's but not on the road, you have to manually shift it. Also second gear is a slow bump kind of shift, and third is binding a little like second is not releasing quick enough.(I did put the stronger spring for the servo release) First thing I did is check the governor and it was perfect, also the governor tubes are in snug. Modualtor valve moves free, all the valves in the valve body move free none are sticking. I did forget my pressure guage so I don't know whats going on there but it goes right into forward and reverse with no lag. I also put in the Superior kit to upgrade the pressure spring and etc. as well as a new sonnax Boost Valve with o-rings. The only thing that is noticeable to me was where you drill the hole bigger for the 2-3 shift it was drilled almost to big as it is almost into the other hole. Could that cause a problem? One last thing I noticed when driving it, it will also lock the tires up if you manually pull it into low even at a slow speed. Okay any ideas will be appreciated. Thanks...

First thing would be another valve body.

Is there a gasket in the valve body?
If not there should be.

Yes theres a gasket. Thats the first thing I'm searching for in the morning before we yank it back out. It doen't make since, everything air checks fine and the valve body seems okay, but I did tell him to wait till I find another valve body and at least try that before giving up hope. This is just crazy. Thanks