I have a '05 Duramax/Allison truck that I bought new. It has ~3000 miles so it's not broken in yet. I love the truck's smoothness, comfort and power,but I have one complaint that GM won't fix or do anything about.

When and only when I'm pulling a trailer(16ft enclosed trailer, 5000 lbs loaded, more wind drag than anything), in long, rolling hills, the cruise control will let the engine reduce speed down 4 mph beneath my set speed. Then it will accelerate very hard to get back up to speed and it overshoots by 3 mph. This is a killer on fuel economy and is a pain when it is fluctuating by approx. 7 mph. The truck has plenty of power for the load, it doesn't even have to shift down when it "floors it" to get back up to speed. I can hold the accelerater pedal with my foot and hold a more constant speed than the cruise does. But I didn't pay $48,000 to hold my foot on the accelerator pedal.

I took it to my GM dealer and they said it will do that per document ID# 1579256 "04-05 LLY 6.6L Diesel Hesitation or throttle delay-kw LLY driveability pedel performance cruise accelerate apply shift# PIP3272- (Dec 21, 2004)"

I didn't think that was acceptable from a new truck so I called the GM customer support line and accomplished nothing other than "your complaint has been filed"

I am a true GM fan and I love this truck, but if I had known of this problem, I would have gotten the 6.0 powerstroke. This truck was bought for pulling and it disappoints me while pulling but is excellent while driving empty.

Oh, and I was told that an exhaust, intake, and computer controller would nearly take this problem away, but that is $1500 for that kit from Edge and it will void my warranty. Major bummer.

Does anybody have any solutions, input or related issues???? I'd like to get to the bottom of this.

Thanks

 

Sorry I don't have any useful input but I can identify with your frustration and sense of powerlessness in the face of the dealers and GM's refusal to be helpful. And I'll bump this thread back to the top where you might get some really useful comments.

 

I hate to say it , but that is pretty much how it's going to work, and it doesnt
matter what brand vehicle it is. Long rolling hills, of course you can keep a more constant speed with your foot. The truck can not anticipate the upcoming hills Plus, you allways can get better mileage when towing without the cruise, that is, if you can drive.

 

Yup, agreed. I've had lots of cars/trucks in the past 12 years or so, some dodge and some gm brands and thats how they all work. A speed sensor has to tell it that its losing speed and in most small grades like over passes, the vehicle won't lose enough speed to drop a gear, but in extreme grades, it will and once it loses that 4 mph it will kick it up.

 

Thanks for the reply guys!

I could understand the truck losing 4 mph if it went up a quick accending hill, but these are long hills that shouldn't catch the truck "off gaurd". It has plenty of time to react.... I sit there and watch the speedo go down and down before it finally decides to hammer it. I don't really agree that all trucks do this. Dad's 2003 silverado 5.3 truck might be underpowered pulling a particular trailer, but it starts to at least repsond at a loss of 2 mph and will then even find another gear if it needs to. My truck does absolutely NOTHING until a 4 mph loss, then floors it and overshoots. This is what is a real pisser to me A cheaper gasser does a better job for gas mileage issuess than my diesel truck.

A GM rep called me today. I need to call him back tomorrow so I will see what he says.........