GM DOD

ok, so the displacement on demand feature of the new tahoe is suppose to improve gas milage but i've yet to witness any real effect.
situation 1: cruising at 75mph down I-20 the engine only drops to V4 when there is
no load on the motor (going down a slight grade). the way it was originally explained to me was that if you were cruising at a constant speed the motor would drop to V4 and stay that way until a significant demand was placed on the engine. question: was this explained wrong or do i have a bad computer?
situation 2: one would think that at idle or in stop and go traffic <20 mph the motor would also default to V4 mode. however, that is not the case. anytime the vehicle speed is less than 20 mph (maybe 25) the engine is always in V8 mode. that just doesn't make sense to me given that is a time when there is very little demand on the motor. question: again, is this a computer problem or is there some other reason to justify?
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Wind resistance is a significant demand. Does it drop down at slower speeds? I don't have the figures, but I've been told that above 60, wind resistance starts taking more horseower than other factors. I'm sure that gear ratios, aerodynamics and such come into play. I do know the difference on my V6 at 60 is 3 mpg more than at 70 for the same stretch of road.

Seems to me that at speeds less than 20 you need a lot of torque to accellerate. If you drive a standard trans in stop & go, how often do you get out of the lower gears?
I'm curious as to other's experiences.
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What mileage are you now getting on an interstate-trip at say 60-70mph on a 300 mile trip (+/-)? s
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first reply: first of all, who in their right mind would tool down the interstate at 60mph? at 70 and even 80 or 90 i get sucked up by faster traffic. i also am not sure how the truck is geared...i knew when i bought it but that info has since left my brain. none of that should matter in my opinion however.....the computer should know that the cruise is set and drop to V4 to maintain the set speed. now, if it would take more fuel to keep the tahoe at 70 in V4 mode than it would in V8 mode i could understand but that kinda defeats the whole theory of DOD.
second reply: i drive from jackson, ms to marshall, tx where i exit hwy 59. this 250 mile section of my trip is all on I-20 which is a relatively flat grade. i get the same mileage in the 2WD 2007 Tahoe as i do in my '99 Z71 traveling around 75mph, rpm right at 2K.....about 18-19mpg. both are 5.3L V8.
sdlomi2 wrote:

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The reason I asked what mileage you get at 60-70 mph(meaning 60 TO 70 mph): I have a friend who often drives a mostly-interstate trip of about 250 miles to Myrtle Beach in I believe a new Yukon with the DOD system. On this I-state one pretty much has to drive very near the posted limits, often below due to traffic, esp. due to all the small towns which are poor and money-hungry for traffic fines. He recently told me about his mileage, and I thought it'd be a good idea to compare what he 'calculates' to what you get. sdlomi
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You might want to reconsider your speeds over about 75.
The Highway Patrol came under investigation a couple of weeks ago, and they are embarassed. Seems some of them may have been sending citations to obituary addresses, because they were issuing suspiciously fewer tickets than expected.
Coming back from Houston (toward Marshall) the other night, they were EVERYWHERE, and ticketing even minor violations.
I always try to drive 65-70, no matter what the scofflaws are doing.
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