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redeyeguy 07-08-2005, 02:52 AM Just got my new 2005 CC 2500HD SB D/A 2 days ago and lovin it so far. One thing that I was surprised about were the RPMs at hiway speeds, when doing about 110km/h or 65 mph I am turning approx 2200-2300 RPM. This seems high with a 5 speed and 3.73s. The reason that I consider this high is that my last truck had a 4 speed trans with 4.10 rear end and at the above speed I would be at approx 2400RPM. Just curious if you are all experiencing the same......... 2zuks 07-08-2005, 03:47 AM yep. it needs another gear. Kessler Farms 07-08-2005, 08:20 AM I've got the ZF-6 and still turn greater than 2K at highway speeds. 2300-2400 RPM at 75 mph. Larger tires will bring your RPMs down a little, if you choose to go that route. lakingslayer 07-08-2005, 09:54 AM I have the factory tires and I run about 1950-2000rpm at 65mph. Factory tune and 3.73 gears. dwrat 07-08-2005, 10:13 AM tires will make an easy rpm and look change. craig64 07-08-2005, 10:51 AM My 05 also turns around 2000 rpms at 65. Normal if you ask me and to has 3.73,s. Deadeye 07-08-2005, 11:09 AM I've got the ZF-6 and still turn greater than 2K at highway speeds. 2300-2400 RPM at 75 mph. Larger tires will bring your RPMs down a little, if you choose to go that route. Drivin' to Indy (2200 miles) w/ ZF6 + 35" tires at 70 mph the rpm was 1,920 downhil and 1,980 uphil speed and tacho reflashed and then verified on trip with gps TxChristopher 07-08-2005, 11:23 AM 65mph should be 2000rpm if stock. His numbers must be off. Converter locked out? GS340 07-08-2005, 12:21 PM my new 05 at 65 is around 2100rpms. You are fine. Get larger tires. Rob147 07-08-2005, 12:30 PM 2000 RPM is normal at 65 MPH with stock tires. However, if the transmission fluid is below about 50 degrees, the TCM will delay TC lockup in fifth gear for a few miles, until the fluid warms up, and you will see about 2300 - 2400 RPM's at 65 mph. This time of year that isn't likely unless you live in nothern Canada or Alaska. If you do live in a cool climate than waht you are seeing is normal, but the RPM's should drop after a few minutes to the normal 2000 at 65. 2004 2500Hd LLY CC SB redeyeguy 07-09-2005, 11:27 PM Well it sounds like things are normal for the truck through replys and a little chit chat at the water cooler. Thanks guys. bullydog 07-10-2005, 02:47 AM Running 265/75 on the original rims and going exactly 107kmph (66.5mph) gps verified speed at exactly 2000rpm. That resembles about the speed shown on a stock duramax as being at about 68mph. But then again, DEPENDING on the tire you chose you might lose the savings in fuel with lower rpm again due to higher friction...:muahaha: Later. rustynuts 07-10-2005, 07:20 PM But then again, DEPENDING on the tire you chose you might lose the savings in fuel with lower rpm again due to higher friction...:muahaha: Later. are you saying you'll see lower mpg's with a taller than stock tire because of added friction???? :Pshyco: Bob Anderson 07-14-2005, 01:37 PM My 05 also turns around 2000 rpms at 65. Normal if you ask me and to has 3.73,s. Me Too:cool: | ||