I've just returned from a nice relaxing trip down to the Carolinas, took the Harley truck for it's maiden long voyage and here's the results.
Total distance driven: 4330 kms / 2691.8 miles
Total fuel used: 129.57 imp gals
Average fuel economy: just under 21 mpg or whatever that is in ltrs/100km.
My truck has a Magnaflow 16616 Cat Back exhaust, AFE Stage 2 CAI and the Gryphon programmer running an 87 octane perf tune.
Overall I am very pleased with the results especially since my highway speeds were usually 8 mph over the posted limit to a max of 75 mph.