guages
Most important is the Exhaust gas temperature. You want to avoid long durations above 1200 degrees. This is real easy to do when you're towing a trailer and going up steep inclines. Taking the trans out of OD or easing up on the throttle will reduce the EGT's and still keep you up with traffic.
Next most important if not as important is trans temp. Keep it below 220. Most summer towing or even driving in the north east has the temp range from 180 to 210. Agian those steep climbs and stop and go will tend to get the temps up a little. If the temp gets above 220, time to change fluid. From what I have read the higher temp will degrade your trans fluid. Least expense is to change the fluid vs. change the trans.
Lastly turbo boost. Fun to watch the turbo spool up. More boost =higher EGT. Stock PSd will hit 15 to 18 pounds. A Psd running an SCMT will increase boost to 25-30 lbs.
Hope this explains



