I have a CAT ACERT engine in my 2007 W900L...and sometimes they get a bad rap...but I love the performance and mpg with mine. I have a C15 475, pulling dump trailers and hoppers. With my half round MAC dump I get around 5.9 to 6 mpg and with my hopper I average almost 6.5. AND I do have a PDI Stage 1 tune which cuts most of the variable valve stuff out and lets it run more like a true engine. I have not put it on the dyno but the PDI guy tells me I ought to be getting around 600 hp to the ground. I think if you get a CAT engine and have it tuned properly by PDI or another reputable after market engine builder, you'll find great performance and good fuel mileage. Just my two cents worth, I hope it helps.
