Better to upshift or not when towing?

[shadoow]

i've got a 2008 GMC 2500 HD D/A. The trans has the 'Tow/Haul' mode for towing heavy loads & I use it when towing the RV. As i go faster the trans upshifts until i'm doing around 60 mph in 5th gear. If i go to about 62 mph, the trans will upshift to 6th. Oftentimes i like to travel at 60 mph. My question (finally) is whether it's better for gas mileage and/or strain on the trans, to go 60 mph in 5th gear or go a little faster to get into 6th gear, then go back down to 60 mph? The trans will downshift to 5th gear if i reach 55 so i'm asking assuming i'll be able to stay above 55.

[More Power]

Fuel economy will likely be best when running at 1800-rpm. While towing, it's best (for fuel economy and driveability) when the trans doesn't shift up/down frequently, but the Allison programming will prevent busy shifting anyway.

Your Allison has a manual mode, which will allow more precise control over shifting. Try a couple different strategies to determine which works best for your particular situation.

Jim

[DmaxMaverick]

I agree with Jim. Try different approaches, and go with what works with comfort and economy.

What is your concern, and reason for the question? Are you concerned for the health of the tranny? If so, discount that as a factor. It isn't likely you will do anything to shorten its life, at or near OEM power levels, anyway. The Allison tranny is a completely different animal, compared to "antiquated" trannies. They just don't fail with any regularity. Keep it happy with service, good fluid, filters, keep the temp out of the red, and don't look back. The PCM/TCM torque management won't let you do anything to hurt it, physically.

[hrsedrvr]

recently to local allison shop for fluid and filter change and this guy said the same thing. that tranny will not hurt itself, as long as regular maintenance is done its bombproof. he said the trannys in the duramax are almost identical to the ones used in school buses. the only problems are when too much power is added. he also said that the 5 spd can be changed to a 6spd quite easily with a new switch and a small change in the valve body and can be done without taking it out of the truck. its mostly just computer work