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2007 Cruise Control Problems - increasing speed down hill

11 messages,  Last post on Jun 23, 2008 at 9:59 AM

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What is this discussion about? GMC Yukon, GMC Yukon Denali, GMC Yukon XL, Performance Mods, Electrical, Truck, SUV

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#2 of 11 Re: 2007 Cruise Control Problems - increasing speed down hill [jan63] by ahightower May 10, 2007 (5:10 pm)
Replying to: jan63 (May 10, 2007 2:07 pm) I have an 05, so maybe it doesn't apply. But I will concur that it, and every other car I've had, will downshift and use engine braking to maintain the set speed downhill. It'll increase some, maybe 3-4 mph before anything happens, but it does do something.
#3 of 11 2007 Cruise Control and Accelleration Problems by kvfallon Jun 10, 2007 (5:08 pm)
I have a 2007 Yukon XL Denali and have a problem with hesitation while trying to accelerate while going uphill. This occurs mostly from a cold start. I also have problems with the cruise control functioning properly; on the highway while accelerating it will jump and kick in violently and it also "jumps" and accelerates too much while on the the downside of a hill. Does anyone else have these problems and what did you do about it? I have taken it to Lou Sobh GMC in Atlanta and they say there is no problem. Replies to this message: jan63 (Jun 13, 2007 8:18 am)
#4 of 11 Re: 2007 Cruise Control and Accelleration Problems [kvfallon] by jan63 Jun 13, 2007 (8:18 am)
Replying to: kvfallon (Jun 10, 2007 5:08 pm) I have taken my to the Chevy dealer where I purchased my GMC 2007 (used) with no luck. They said it's common and due to fuel savings it can fluctuate. I was not satisfied with the answer so I emailed GMC. That was no help. GMC called the dealer and then called me back saying what the dealer already told me. ????? I am taking it to a local GMC dealer next week. I gained 12 miles down hill - it is as if the cruise kicks out on the decline. And on the incline waits until it is below the speed and had to really accelerate to meet the set speed.
#5 of 11 2007 GMC 2500 Runaway downhill trailering by carclo Jun 28, 2007 (10:00 am)
My brandnew (412miles!) GMC 2500 pulled my 4 horse trailer perfectly up a winding steep grade to my favorite trailhead. But the trip back home was wild. In LOW, I had to go to my brakes more than every 10 seconds to keep my speed down. That trailer pushed me ever-faster down that grade. Either the Low gear is not low enough, the Vortec engine doesn't allow enough compression for braking, or I need a different ratio. I have a 3:1.. but my dealer says that likely the 4:1 will pull uphill better but NOT give me more braking! Anyone have any comments? Any solution? My old 1991 GMC would crawl down that same hill in Low. I think the cruise control problems are related to a downhill engine/gear braking problems.
#6 of 11 2007 Denali XL Cruise Control downshifting problem by colonelz Aug 29, 2007 (12:20 pm)
My 2007 Denali XL will downshift too quickly when going up the slightest incline, sometimes even two gears - increasing revs unnecessarily and wasting fuel. While I know a six speed has closer shift points, I just do not think this is normal, especially on gradual inclines. Anyone out there have similar experience or know of a GM fix in the works? Other than that, it's a great vehicle (so far). Replies to this message: brewboy (Aug 30, 2007 9:45 pm) colonelz (Aug 31, 2007 4:50 am) brewboy (Aug 31, 2007 8:58 pm) and 2 more...
#7 of 11 Re: 2007 Denali XL Cruise Control downshifting problem [colonelz] by brewboy Aug 30, 2007 (9:45 pm)
Replying to: colonelz (Aug 29, 2007 12:20 pm) I have an 2007 Denali build date March 2007 and it does the same thing. According to some on another forum the best solution is to reprogram the engine and transmission with a Diablo Sport Predator programmer ($300. I have been told thats what GM did to the Escalade when they set up the 6.2L L92 engine for 403HP as opposed to our 385HP. Replies to this message: colonelz (Aug 31, 2007 4:50 am) brewboy (Aug 31, 2007 8:58 pm) colonelz (Sep 03, 2007 4:51 pm) and 1 more...
#8 of 11 Re: 2007 Denali XL Cruise Control downshifting problem [brewboy] by colonelz Aug 31, 2007 (4:50 am)
Replying to: brewboy (Aug 30, 2007 9:45 pm) Thanks! Does your Denali downshift even at the slightest incline? I have not noticed the problems going downhill like the others have, but the uphill, or better defined, up gradual incline shifts drive me nuts!   Do you have a link the the other forum? Also, will applying the programmer void the warranty? Replies to this message: brewboy (Aug 31, 2007 8:58 pm) colonelz (Sep 03, 2007 4:51 pm) colonelz (Jun 23, 2008 9:59 am)
#9 of 11 Re: 2007 Denali XL Cruise Control downshifting problem [colonelz] by brewboy Aug 31, 2007 (8:58 pm)
Replying to: colonelz (Aug 31, 2007 4:50 am) I find it actually tries to hang on to 6th gear on slight inclines and then actually engages in what GM calls "Busy shifting" they put out a TSB on that with a fix you may wish to investigate.   Document ID# 1892711 6L80 Auto Transmission Busy Shifting, MIL Illuminated, DTC P1751 Set (Replace Control Body Spacer Plate) #07-07-30-002-(01-30-2007)   Its says vehicles built before December 2006 but I think I still have the problem.   The programmer plugs into the UDC connection under steering wheel and when you take vehicle for service you just re-enter the OEM program and the truck is back to factory settings.   The other fourm is The Chevy Avalanche Fan Club Replies to this message: colonelz (Sep 03, 2007 4:51 pm) colonelz (Jun 23, 2008 9:59 am)
#10 of 11 Re: 2007 Denali XL Cruise Control downshifting problem [brewboy] by colonelz Sep 03, 2007 (4:51 pm)
Replying to: brewboy (Aug 31, 2007 8:58 pm) Thanks, I will get with my local GMC dealer who seems to really want to please their customers. Will keep thread updated! Replies to this message: colonelz (Jun 23, 2008 9:59 am)
#11 of 11 Re: 2007 Denali XL Cruise Control downshifting problem [colonelz] by colonelz Jun 23, 2008 (9:59 am)
Replying to: colonelz (Sep 03, 2007 4:51 pm) Took a trip this weekend (about 200 miles) in the 2007 Denali XL and noticed a improved (although not perfect) cruise control performance. Very little downshifting while going up gradual grades, 17.2 mpg with a/c on, traveling about 68-75 mph.   Difference??? The only thing I did was increase the tire pressure (20 inch rims) from 34 to 38 psi.

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