The cummins Disco was getting in the high teens, correct? It’d be interesting to hear real world mileage— I’m guessing 20 or below based on what I’ve heard so far, but I am interested as the 2.8 is on the table for my next build...but not at those levels. I’m hoping it’s considerably more...
Running with the defender speedometer buried, turning 2900 +/- rpm, I got 21-22 across Kansas and Eastern Colorado. I had to get to the Denver airport to meet the owner we'd done the conversion for, so was running hard, very hard, over 80. Driving it 10-15 mph slower would make a large impact on mpg. Gearing, tire size have a great deal to do with mpg.
The early automatic trucks like the disco built by Heritage Driven and a few others utilzed high rpm stall converters to put a bandaid on the early programming issues. Because of the high stall converters used in those installs there is considerable slip and mileage sucked.
We have come along way chasing the ultimate program for the 2.8/6l80e. We built the first one in a defender (didn't use a high stall converter) and aurguably have more hours/miles run time on highway and off with a 2.8 auto setup than anyone else. There is considerably more to it than just saying x platform got x mileage.
Looks like we have three R2.8 auto builds to do this Spring, all 110's. We will be playing with programing quite a bit. Auto mpg has a great deal to do with the programing. Sharper shifts and less torque converter slip= higher mpg but not necessarily what most owners desire. There are around 10,000 program adjustments possible on a 6l80e.