LOW EMISIONS LEAK, I PUT ON A NEW GAS CAP BUT CODE CAME BACK ABOUT 4 DAYS LATER. I WILL CHECK HOSE TO CANISTER DUE TO OTHER POSTS, BUT WOULD A VAC LINE LEAK CAUSE YOUR MPG TO DROP ALOT. I PUT ABOUT 150 MILES ON MY TRUCK LAST WEEK AND WENT THROUGH A FULL TANK. COULD IT BE THE O-2 CENSOR? I GUESS THERE ARE 2 OF THEM AND I DO NOT KNOW IF I WOULD NEED TO REPLACE BOTH? THANKS FOR THE HELP.