Transmission Tow/Haul mode kicking in

[mwool]

I have a 09’ 3500HD Diesel w/@5000 mi… What I am seeing appears to be the transmission in the Tow/Haul mode kicking in without me pushing the button and it not lighting the display light. Let me explain. I can be driving and the displayed MPG hovering at 18. Sometimes but not always after I stop and turn off the engine for a short period of time, after starting, the MPG begins dropping rapidly even at a constant speed and coasting. It will go down to about 10-12 MPG before stabilizing. I have discovered that when the MPG begins to drop rapidly, if I enable the tow/haul mode and the light on the dash goes on and then I turn the tow/haul mode back off and the light goes off, my MPG stops the falling and starts back up again. Any clue what might be causing this?

[DmaxMaverick]

Welcome aboard!

DPF regeneration. It will keep trying to complete the cycle until you let it. Driving habit and messing with the T/H mode during a cycle can cause a delay, and a repeat. Get on the highway, set the cruise and let it complete (ignore the DIC during the process). You may see this more often with more slow/stop/go driving (city). You may seldom see a cycle if you tow often.

[mwool]

DmaxMaverick thanks. Yes as you mention I have of late been in more slow/stop driving. In thinking about past mostly highway driving I do not recall seeing this effect. As I am new to this truck could I get your thoughts on – I do have a Banks 6 gun. For this slow/stop driving mode, is it better from a stop to get up to speed (go through the low gears quicker) sooner vs creeping up to speed. This is when not towing an RV. I am typically same or slightly faster off the stop light as others although I get passed before the next light. I ask because Banks told me to be heavier footed from the lights. I had not thought about these driving habits effecting DPF.