applogies if I overlooked a thread where this was already discussed. I'd like to know where the CTD likes to run when pulling -- the subject of the day is whether it will like my 285/75 tires. with the NV5600 tranny, I run at about 1800 at 65 mph. Is that high enough to tow at 65 mph? I have Stock fueling (ETH) except for the EZ box. As regards the towing rpm, I'm tempted to add fueling (hook up the pump wire or add injectors) so that I can run at the prefered rpm and optimize fuel economy. Will that yield better or worse mpg than raising the rpm via smaller tires? I haven't towed yet, as you can see :-)<br><br>I noticed that the 03's come with 3.73 gears. hmmm.<br><br>

 

I try not to go below 1800 rpm when towing. Even with my mods and 4.10's, it doesn't really come on the pipe until 1700 or so. I personally believe I see better mpg when towing in sweet spot rpm. Sweet spot being 1800- 2300, and upshifting @2500, your left leg does get kinda tired though.

This is towing a 31' sprint car trailer, raised roof, front observation platform with rails. 11' tall at rear, about 18k loaded

 

Max torque for the stock ETH is at 1600 rpm, anythiing above that works for me, depending on EGTs. Sweet spot seems to be between 1800 and 2000 rpm.

 

Doug,<br>You didn't give enough info - - what are you wanting to tow? If you want to put on a heavyweight 12' tall, you might have a problem. I am running a 4.10 on a 2003 HO 6 speed. I sure would not want to turn any slower in sixth than I do - - I am very happy with the 4.10. I would really think hard about effectively raising the ratio with larger tires and still wanting to tow.

 

I'm looking at tall ~30 foot 5vers in the 10,000-13,000 GVW region -- just under the 20,000 GCWR rating of the 02 ETH/DEE. When you said 12' tall my brain went &quot;oh yea, wind resistance. <br><br>anyway, with 3.55 gears and the 6-speed things are very happy running empty with my 33&quot; 285s -- I got 19.7 mpg over a 500 mile stretch last week, going though central Idaho from N to S on highway 95 at ~ 65 mph. But over the course of this trip my &quot;running empty&quot; frame of mind shifted to towing and I thought more about heavy loads, gears and rpms. 65 mph is a touch over 1800 rpm and switching back to 265's would put me closer to 1900. that would probably be good. For harder pulling, I'd expect to run at 55 mph in 5th gear. thats touch over 2100 rpm with the 285s and closer to 2200 rpm with 265s. For the really hard stuff I can drop to 45 mph in 4th gear and turn a bit over 2400 with 285s and close to 2500 with 265s. <br><br>Part of my question has to do with the tradeoffs of adding power enhancements versus gearing down. So I'm out to understand where the CTD likes to work hard, from a fuel economy standpoint. where is the sweet spot, and is it different for empty versus towing? If you're cruising on the freeway pulling 12,000 lbs, where should the rpms be to maximize fuel economy? If it is 1900, then I can achieve that by switching back to 265/75 tires (if I want to run at 65), and if I don't have enough power at 1900 I'll add injectors. But if guys are getting better economy pulling at 2100 or something like that, then I'll start wishing that 3.73s were available as on the 03s. Not sure I'd put 4.10s in, as this truck has to do more than tow the family to vacation spots. its also my daily driver goes offroad, and makes empty trips as well. <br><br>