I'd change all 6 spark plugs.

If you're getting a misfiring coil just change the one that's missing for now, but visually inspect all for damage, etc. Clean the contacts with electrical cleaner and put some dielectric grease on the harness.

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2018 Ram 2500 6.7L Cummins 68RFE
19k miles -Bright White/Black - Big Horn Sport - Crew Cab Short Bed
2013 X5 35D (CEO's) - Born on 5/17/2013 -
82k miles - Alpine White/Cinnamon Brown/Premium Pkg, Sport Activity/Premium Pkg and Sound/20" Style 214/Running Boards