I get that you don't want a diesel, and that's fine. But since you seem to be a mileage junky, I'll mention this. My 2000 dodge 2500 24 valve 5 speed cummins will get up to 28 mpg on highway trips even loaded with no trailer. I use a scan gauge II which pulls info from your obdII and this scan gauge is known to be quite accurate. Now when I pull my 20ft enclosed weighing in at 10,000 lbs and driving through the stop and go city traffic, the mileage is 12-13. I am 26 and no light foot either. My repairs have been limited, and IMO if you are a mileage junky, the 5.9 cummins is the only truck to have. Imagine if you only had to pull that little trailer around with a truck that gets incredible mileage.
2004 Ram 1500 Hemi
2000 Ram 2500 24 valve CTD
1996 Ram 2500 12 valve CTD
1999 F350 7.3 PSD flatbed
20' enclosed, 16' open, 14' dump
2 Walker MT 48", Toro Z500 60",
Toro proline 48", Dixon ZTR 42"
Stihl small equipment
SC licensed pesticide applicator