Originally Posted by
Edahall
Either a GM 6.2 or Cummins 3.9 4BT. Do you have overdrive? The 6.2 likes to cruise at 1800 rpms and Cummins is a bit lower like 1500-1700 rpms. The 4BT would likely yield better fuel economy. However, a 6.2 that is set up with fuel economy in mind can yield close to 30 mpg.