3.73 vs 2.89 ratio with a Detroit ??

Old Man, both of those engines would meet the '98 EPA emissions standard. That was the "LoNox" you referenced. They would both have the low nox programming. They would not necessarily have a LoNOx sticker. If they have an EPA '98 sticker, which being 2000 and 2003 engines, they would, then that is the same as a LoNOx sticker.

I do side with you on the getting the ECM reprogrammed. That can either be done by someone or you can get something like the Bully Dog Tuner and do it yourself without removing the ECM from the engine or having to drive somewhere and have it done. Bully Dog is really expensive though. Rebel127 here on the forum can do it a lot cheaper.

 

i have the old swift combo

12.7,Detroit, 2.93, 13spd, 22.5 LP, and i get 6.6 avg all day running between 65 and 70

 

Remove the ECM, send it to be reprogramed while truck is being made into single axle, no time lost, fuel savings from day one.

 

It should get 8+, if not check CAC, air filters. Check tires for rolling resistance http://locator.michelintruck.com/RRListings.aspx, and run overhead.

 

Yeah it should get into 8 mpg on a regular, consistent basis. My rebuilt 12.7 500 hp DDEC IV with stock programming, 18 speed, twin screw will consistently get in to high 7's average on all loads during summer months. With lighter loads, I have no problem getting into low 8 mpg territory, pump to pump calculated. But I am also using ported/polished/coated exhaust manifold, BW 171702 non gate turbo with a blanket, high flow Walker mufflers on the stacks, and a Fleet Air Filter on the intake. The ECM reprogramming is a good idea, and I will be doing something in that regard this spring, but to get the most from it, also making some mods to the intake and exhaust side will really make a major difference to bring out the effectiveness of a tune.