[93tracerwagon]

Recently purchased a Chevy 2500 Full Size van with the 2.8 Duramax, 8 speed Allison auto trans. Fuel mileage is really impressive. I have about 5000 miles on it, running about 7500 lbs to 8000 lbs GVW. With a full tank of driving in city of Chicago traffic (no burbs) we are getting about 21 mpg. Just took it out on a short highway trip and it's getting about 27 mpg at 65 mph and about 31 at 70 mph. At about 67 mph it upshifts and rpms drop from 2100 to 1500.

I've also noticed it appears the trans is programmed specifically for heavy loads.... it holds low gears for a long time before upshifting.

I don't know much about diesels, so any input would be helpful. I suspect engine loads are closely monitored by the electronics, so if I do some aero modding (probably a front undertray and reduce amount of wasted air going through the grill and not the radiator), it may upshift at lower speeds on the highway and be able to hold high gear at lower rpms. I imagine if I can hold high gear at 60 to 65, I could be running about 1400 rpm on the highway and pulling down mid to upper 30's MPG's

Is there any place that has the factory CD for these vans. It's nice to know where I'm starting.