Just made a little jaunt with the CTD, about 300 miles each way near all highway. Note: I have stock rubber & 4:10 gears as in my signature. (IMHO, 4:10 ratio is too low unless you're going to put big rubber on it, but I own it now.)At 65.... 2000 rpm... was getting 17.8-17.9. On the way back, I dropped the rpms to 1900 & speed to 60 & mpgs went up to 18.2 With my stock truck, the overhead has always been right on. These are running right foot on the pedal, trying to get mpgs... cruise control does not feather the crest of hills & gets a bit less mpgs in my truck. Russ

I find my biggest mileage numbers holding it in 6th on the highway at 1600rpm. I have 3.55 gears though. However if the truck has to pull a decent amount of weight I would drop to 5th and raise the RPM's to 2000-2300rpm to keep the exhaust temps down.

In the past, I've improved my mpgs on secondary routes by getting the auto to shift up into OD then using minimum rpm to keep it moving as traffic & road conditions permitted... running light, of course. Admittedly, the auto would correctly shift down for minor hills but that was expected. Buying the truck with wrong axle ratio was a blunder... Russ