DT12 on highway vs vocational transmission

I've never heard of a Vocational aspect to a DT12
Are you taking about Economic Mode vs Performance mode? The DT12 has a Performance mode that is selectable by steering wheel column but carriers will lock this out leaving you only Economy and Manual. They'll tell you it only reduces the RPMs to save fuel but the thing about the DD15 is that it's a variable torque engine and i can assure you that Performance Mode uses all its power across the spectrum and it uses more fuel accordingly. Frankly in the vocational sense, say day cab city delivery, it's just more feasible to be in Economy mode than roaring through the gears from light to light. Economy may start of in 5th and select 8th next. I like Performance on the highway in the hills. Where you can maintain some speed with a little drop rather than 75 down to 50mph if I can hold at high 60's.
Hope that helps.

 

Unless you're doing off road work, heavy haul, or PTO work the vocational version is going to be overkill. Even if highway mpg remains the same, you'll be paying for features you're not using. It would be like specing out an 13 speed for local pd work.

 

Cool . My apologies. Never heard of it until now. Very impressive.

 

Ya don’t need a 18 speed if you only grooming 80k on paved roads.
I never split bottom gears grossing 140 k in the bush if the road bed is solid