[Diesel_Dave]

Interesting, have you compared your fuel consumption in terms of gal/ton-mile between the two trucks?

The temperature thing perplexes me. Is that info from the Cummins manual or PACCAR? I do know that many of the newer diesels with SCR systems have a "warm-up" mode. The issue is that the catalyst doesn't work until the temperature gets above a ceratin threshold (just like conventional 3-way catalytic converters on gasoline cars). Basically, the engine is trying to get the cat hot ASAP so it can start using the DEF to cut down the NOx. However, there's no reason that the truck can't be moved while it's in the warm up mode--if anything it helps it warm up because adding load helps it warm up sooner. So I'm not sure what that's about.