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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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#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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