I think the difference in the LSD and ULSD is for the soot build up. I have 150k miles on my 6.7L. I have ran LSD, ULSD, Fuel from Mexico, etc and haven't had any fuel issues. I would just suggest maybe changing the fuel filter more ofter. I change mine every 10K but that will soon be obsolete as I will be installing a FASS 150gph from K2 in the next few weeks. I think my stock pump is getting ready to crap out on me.
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2007 6.7L QC DRW 4x4..... Custom Built 68RE by DPT ..... 5" BADP TBE, EGR & Cooler Delete, Edge w/Attitude, MP-8, Firestone Airbags w/ Dual Control, AFE Filter, 100 gal Transfer Flow Aux Tank, B&W G/N, Dynatrac Hub Kit, Warn 16.5 Winch, Optima Batteries, Triple Train Air Horn, Amsoil in & out, Full line of Smoked Recon's/Line of Fire/Big Rig Lights.....