I was just researching the 6.7 with the deletes in place, and it appears I spoke too soon. I havent really kept up with 6.7 mods lately b/c I dont own one. It appears the mileage gains are significant.....very cool! Actually better than I first believed. But I just paid off my rig, and Im not looking for a newer CTD with the 6.7. Maybe a 6.7 engine swap when my 5.9 craps out.... Is it possible????

 

Thanks for all the helpful info. As I said before I have a 5.9 12v and it is great. Just wish the rest of the truck would hold up just as good as the engine. I think from what I am hearing the 5.9 is best choice if I don't want to do any modifications if that is the right word. Any thoughts on transmissions? I currently have an automatic in my 98' and have not had any problems. Seems to do ok when hauling heavy loads but I am leaning towards the 6 sp this go round. Any input?

 

It pretty much comes down to preference, in my opinion. Auto for its simplicity, and 6sp for (gear-jammin) choice of gears when hauling or pulling hills/grades. I prefer auto's myself. Tried manual, but didnt like constant shifting, especially in heavy traffic (used to live in Southern Calif). My dad has the same year truck as me, only manual trans. He hates auto's.
As for mods to your 12v, If ya wanna just improve efficiency, a good free-flowing 4" exhaust system. For intake, also free-flowing CAI kit or homemade kit with hi-flow air filter or BHAF (Big Honkin Air Filter). You can also bump up the timing and "turn up the screw" on your injection pump for a bit more fuel and power. I dont really mess with 12v, but im sure a 12v guru will chime in for additional info.

 

Right on the money bigg redd

 

Thanks bro!

 

i love my 03 5.9 list what i have done to mine it pretty good for towing if your looking for speed then 6.7 is the way to go i kept my 5.9 stock pretty much and i tow three and 6 place horse trailer with problem just came back from ohio just last night love the truck only have 125,000 on it

 

I've got an 07' with a 5.9 and LOVE it! However, a friend of mine has an 08' with a 6.7 (deleted) on 35" tires and can get 24-25 mpg on the highway. If it says Cummins, I don't see how you can go wrong. I do know this, the is no substitute for cubic inches.