Keep your OVERDRIVE ON and just drive normal... without going over 2000RPMs that is... I’m in overdrive by 35MPH... And as soon as the OD locks I use the cruze control button to accelerate up to speed.... Trust me, this will save you fuel!

Keep your highway speed to or about 65MPH, and stay out of the passing lane. I know allot of you guys feel the world is passing you by... but your not going to gain that much time driving 10MPH faster... actually your not saving any time. You’re talking the difference of 1-2 minutes tops for most people ... that’s not worth the fuel you used to save those 1-2 minutes... nor is it worth the ticket if you get pulled over. Don’t get me wrong... I like to speed... but I do it for enjoyment, not to get where I’m going any quicker nor do I do it to save fuel doing it. But If I want to conserve fuel I can get over 20MPG by taking my own advice.

Also when possible coast to a stop. If you know you need to stop at the light/sign and you have enough speed to coast to that point then just throw your shifter into NUTRAL and coast to that stop. This will save you allot of fuel in the city alone.

Insure your tire pressure is good. I like to set mine to 5PSI below the max... I used to set it to the MAX but my tires would ware too quickly. This is good for 1MPG easy opposed to too low inflated tires.

SPEED SAFE, AIR RAM

 

If this does work for you then it just means you’re UNDER GEARED. The only reason it would save you fuel by turning off the OD is if your gearing was too high. 3.55's combined with the .67 overdrive leaves you with an overall ratio of a 2.37 gear when you do make it into OD... which is painfull for a an engine trying to move 6000+lbs at 40MPH. So your engine can not even take the OD untill you have enough RPMs to hold that gear. At low RPM’s that 2.37 gear ratio will increase the load (MORE FUEL) on the engine... so it needs to downshift to a lower gear in order to lessen the load (LESS FUEL) on the engine. Although the RPM’s increase the load is lessened and the Fuel economy improves. If you find that turning off the overdrive in the city is improving your fuel economy then you should look into a new set of 4.10's or 4.56 gears. With 4.56's you will have an equivalent of a 3.05 gear ratio, this will lessen the load and increase city/highway fuel economy up to 65-70MPH....

Many people have made the switch from 3.55's to 4.56's only to gain increased fuel economy and off the line pulling/acceleration.


SPEED SAFE, AIR RAM

 

I am not sure about the gas milage but I just had my tranny rebuilt and went real beefy. The trans shop told me to leave O/D off around town and not to put it on untill I get around 60mph. We have alot of traffic here so in O/D it is constently shifting up and down in traffic and they told me that is not good for these trannys.

 

The reason the OD would be bad for your transmission is the LOAD it has to deal with when in the taller gear. This is another reason GEARS would be the correct FIX for that problem... move the mechanical advantage from the transmission to the rear end... this means all the stress the transmission sees in OD would be moved from the Trans to the rear end... and the transmission would run cooler and live longer… Its like changing gears on a 10 speed bike.

SPEED SAFE, AIR RAM

 

From the 04 manual for you sceptical types.

TOW/HAUL OVERDRIVE SWITCH DESCRIPTION
The tow/haul overdrive OFF (control) switch is located in the shift lever arm (Fig. 106). The switch
is a momentary contact device that signals the PCM to toggle current status of the overdrive function.
OPERATION
At key-on, overdrive operation is allowed. Pressing the switch once causes the tow/haul overdrive OFF
mode to be entered and the Tow/Haul lamp to be illuminated. Pressing the switch a second time causes
normal overdrive operation to be restored and the tow/haul lamp to be turned off. The tow/haul overdrive
OFF mode defaults to ON after the ignition switch is cycled OFF and ON. The normal position
for the control switch is the ON position. The switch must be in this position to energize the solenoid and
allow a 3-4 upshift. The control switch indicator light illuminates only when the tow/haul overdrive switch
is turned to the OFF position, or when illuminated by the transmission control module.

NOTICE: It can't shift from 3rd to 4th, let alone 5th.

 

All the above applies unless you have a six speed stick------like me!!

 

Just checked my manual, it is different than yours. mine is a 2005.

It says "When operating in tow/haul mode, 5th gear(if equipped) is disabled and 2-3 and 3-4 shift patterns are modified. Shifts into Overdrive (4th gear) are allowed during steady cruise (for improved fuel economy) and automatic closed throttle downshifts to 3rd gear (for improved braking) will occur during steady braking."

It does say to use tow/haul if you encounter frequent shifting, maybe I should try towing without it first. My main complaint is that tow haul tries to use 4th gear when I think it should be in 3rd. Maybe with tow/haul off it will use 3rd gear more, like I want it to.

Im jealous of you guys with 4.56 gears. But I am afraid to make any changes during the warranty, especially with the track record of these rearends.

 

If tow haul dosnt allow the truck to shift into overdrive, why does my truck run under 1800 rpms going 60Mph? I have 3.92 gears in the rear by the way.