I have a 53 1 ton panel. I changed the rear pumkin to 4.10,run 235/85/r16's and swapped in a T5 from a Camaro. I rebuilt a 261 and have a holley/weber 2bbl on it. I run 1900 at 55mph and with 2100 miles on the truck I'm getting 13-14mpg in town and 17-18 on road trips. Clutch and tranny cost about $250 and the rear end was $150.
Most of my driving is at 45-50mph with rpms in the 1500-1650 range.
I guess you just have to balance costs vs. labor time. My setup was an easy job.
