I average 14-15 mpg in mine (2000 4.2 w/5-speed). Part of it is my lead foot and the other is the 305/70's under it.

 

2001 4.2L 5speed 4x4 RegCab 19mpg tank after tank

 

i've got a 98 4.2 5-speed. I get anywhere from 10-13... most of it's city. But it's not that sluggish, sure, it may be if you like to tow stuff... but it's not that bad. the only v8 truck to ever beat me in a race was a v8 tundra. and it wasn't by much.