Check these guys out.
DeLuca Fuel Products They sell CNG conversions. I'm waiting on a call back from them for some more info.
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08 2500 6.7L Mega Cab Laramie 4X4-8" Rize lift w/Pro Comp 37x13.50 Xtreme A/Ts and 20" Driv Devilslides-Volant CAI-Edge HOT w/Attitude-TS MP8-BW Fender Flares-BADP 5" DPF delete-EGR gone-Siege Eng. train horns-6000K HID fogs and headlights-Airdog 150