[mguay]

If you are worried about temps in you trans...a switch to Syn is a must. Your dealer's trans tech probably just hasn't tried it as GM doesn't make a Syn trans fluid. Dex 6 is not Synthetic. On my last 2 Allisons I have flushed the dino oil from them at the 2500 mile mark. With the dino while towing, the trans temp would go to the 180s. After the switch to a full Synthetic...the temps never g over 145. Your 6 spd is not an Allison, so it may be a bit different. I had an 09 gasser with the same 6 spd and the temps would run around 210 while towing in the hills. I was told the overheat msg would appear around 275...which in my opinion is too late.