2007 GMC Sierra Duramax Diesel 2500HD Allison Transmission temperature gage rises and overheats when going up small and large hills immediately goes back down at top of hill or when we turn air off. Also will all of sudden lose power and cant go over 30 miles per hour until we stop shut truck off wait 10 minutes and restart. Any Ideas why this is all of a sudden doing this?:

SOURCE: 2003 GMC Duramax Diesel won't start

I see that you had the injectors replaced 20,000 miles ago. I would still check the oil to make sure it is not overfull. The new injectors could be bad. If the oil level is not overfull then get a paper towel and touch the dip stick tip on the paper towel while oil is on the dip stick. If it's only oil it will not spread. If it has diesel in the oil the oil with spread. If this test doesn't show the injectors to be bad then you have three other possibilities. The FICM (fuel injection control module), the fuel pressure regulator, or the injection pump. It's hard to pinpoint what the problem is without running more tests and the only way to run those tests is with the computer the dealership has. Just so you know your injectors are still under warranty until 100,000 miles. Most likely you will have to take it to the dealership to get you truck fixed. I hope this helps you some.

Wade Cook

• 6 Answers
• Posted on Jan 27, 2009

SOURCE: 4X4 inop on 2003 GMC Sierra 2500HD

I have found that when you are going to engauge 4x4 high, it is best to only be going about 3 miles an hour. Not faster, not stopped. It likes some movement to help it mesh. I've had perfect shifts since I started this. Hope it helps. Wade.

Joe Lamb

• 463 Answers
• Posted on Mar 29, 2009

SOURCE: '03 GMC 2500HD 4x4 problems

Take your positive cable off battery and wait a few minutes..This resets the computer and takes it out of limp mode.Theres been a lot of problems in the dash so if you can find an auto zone and have them scan it They'll do it for free.But as far as the lights my truck does the same thing. Just flick your fingers on the buttons and they should flash..The plug in the back of buttons was loose..

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SOURCE: 2001 gmc 2500 6.6 w/ allison transmission,keeps

You may want to inspect the "pass-through" connector for water contamination, and/or related wiring for corrosion.

SOURCE: GMC Sierra A/C Stops Cooling After Driving a Few Minutes

It sounds like you either have an condensor fan problem or low freon. The condensor fan is near the radiator. In some cases the radiator fan doubles as the condensor fan. So look there too.