[MENTION=448354]ElDuck[/MENTION] Figured I'd chime in - I'm getting low 14's lifted, on 32's, with a rack, bumper, skid, and loaded cooler of Spotted Cow. In sub-freezing temps, no less. OP, you should be getting a tad more. The family '06 V8 in stock form is getting 17 in the same conditions. How do the spark plugs look?
Spark plugs are brand new OEM spec Denso replacements, gapped proper and torqued.. or do you mean pull them and see how they look after driving?