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MNOutdoors 08-02-2005, 01:30 PM I now have 1000 miles on my new GMC 2500HD. At 65MPH w/o trailering or tow haul activated, my RPM is approx. 2300rpm. The DIC indicates 14.1 mpg. A friend who drives a Dodge/ Cummins says the RPM is way to high and I have an overdrive problem. This is my first diesel and know enough to know I don't know. Do I have a problem and need to bring it in? What is the average RPM range. I have 3.73 gears. socal LLy 08-02-2005, 01:36 PM As the dealer would say it's normal.If you put 285-75-16 on it you will see about 2100rpm at 70mph your buddy is driving a dodge so there is no comparasion and to answer your question your truck is fine Big_Gunz_ 08-02-2005, 01:42 PM I've got a 05 GMC 2500HD like yours, completely stock. I have 5000 miles on mine and at 65mph, I run around 2100rpms. I just drove to Vegas and back from SoCal this weekend and got 16.4 miles to the gallon (D.I.C.). Not sure if its something to take in or not, maybe give it some time to break in some more. lakingslayer 08-02-2005, 01:52 PM Don't beleive the DIC unless you hand calculate to see how accurate it is. Mine runs just below 2000RPM's at 65mph with stock tires. A GPS unit should give you a pretty accurate MPH to see if the calibration is off on the Speedo. skoryaro2 08-02-2005, 02:23 PM Not to mention that the Tachometer may be off.......if you think your OD is not kicking-in, push in the OD lockout button (T/H button) and see what happens. Kendall69 08-02-2005, 02:41 PM At 65 floor it and let the speed climb and see if you catch the next gear, then back down to 65 and see what the RPM's are. cowdoc 08-02-2005, 04:22 PM My '05 with stock tires turns 2000 rpm's at 65 mph. Yours sounds high to me. Just my .02. webecrusin' 08-02-2005, 07:44 PM Your buddy is right; your revs are too high for that speed. jwfab1 08-02-2005, 09:55 PM My 05 is around 2000 RPM also at 65. 75 is around 2200 RPM. I think these trannys could use another gear, and apparently so does GM. Thats why the 06's have a 6 speed. Jason dan_diesel 08-02-2005, 09:59 PM just got back from a road trip and mine is in the 1800 - 1900 rpm range at 65, my tires are the stock 265s that come on a 3500 srw. I've found that my DIC is consistently .2 mpg high, btw... YellaCat 08-02-2005, 10:25 PM I think you have a problem with the revs as well, I'm right at 2000RPM at 65 with stock 245's. TC not locking up maybe? I don't think your turning enough RPM to be in 4th but i could be wrong. Mike L. 08-02-2005, 10:38 PM If something was not kicking in as far as lockup or 4th the TCM would have let you know. The Ally lets you get away with nothing. mike TPBGMC 08-02-2005, 11:07 PM My 2005 GMC is similar. I'm at about 2,100 rpms at 65 mph. However, worth noting - according to the new GM press release that details all of the changes for 2006, the new allison six speed includes what GM refers to as a "second overdrive". The press release says that when traveling 60 mph, the engine will be at 1550 rpms & will be much more economical. Timberwolf530 08-02-2005, 11:17 PM Now if we could just figure out a way to unlock the "secret" 6th gear on our older trannys, we'd be set.:muahaha: chevman 08-03-2005, 12:15 AM we have an 05 3500 dooley and 60mph is 1800 rpms. chevman arson guy 08-03-2005, 01:44 PM my 2005 2500 hd cc stock at 1800rmp 55mph 22.4 mpg, at 200rpm 65mph 18.4 mpg low rmps better mpg arson guy 08-03-2005, 01:48 PM :cool2: my 2005 2500 hd cc stock at 1800rmp 55mph 22.4 mpg, at 200rpm 65mph 18.4 mpg low rmps better mpg 10-4 arson guy 08-03-2005, 01:51 PM my 2005 2500 hd cc stock at 1800 rmp 55mph 22.4 mpg, at 2000 rpm 65mph 18.4 mpg low rmps better mpg BigOL3 08-03-2005, 01:53 PM I understand that the final gearing on the ally/zf6 are the same. At 65mph I am only turning about 2000 rpms. | ||