I just fixed this issue on my 05 Hemi WK. I had a check engine light and a "check gas cap" light.
I highly suggest you double check your hoses. I took off my rear drivers sides wheel and fender liner and found this while under the Jeep...
Replaced the hose, cleared codes (check engine light went away) and "check gas cap" a went away a day later (after computer re-learned somethings!)
So I would start with that. Hope it helps.