Air dam / Air foil on cab roof or camper cab over?

Than there is more to operating cost, that fuel.
Somewhere on this forum is a topic from about 8 years ago, where member driving dump truck for a living, decided to rebuild Detroit 8V61.
When the engine is fuel hog, the in-frame rebuild was done for about $3000, comparing to about 10x more for modern truck engine.
That is why I remember that 15 years ago lot of semis were still driving with 318 hp under the hood.