im not complaining about gas, i could care less its worth taking it up the butt to drive my beast

anyways i have stock offroad pakge tires and they seem to loose air fast !! im filling them all up at least once a week.. and my low pressure lights always on...so tonight i go to fill them all up again and put them at 40 hoping it will last a little longer and maybe some better mpg well my front left was at 10PSI !!!! the right was at 20 and the back were 25 30..
i think my valves are going or someone unscrewed the stems some... anyways im going to take her to the dealer tomorow about it probabably...
so anyways anyone know why ? and could this contribute to my 11-13mpg ??? oh and thats highway miles.. 95% of its highway...
__________________
07 TITAN CC,O/R,B/T 4X4 SE
MAJESTIC BLUE
mods: fram boost air 2 cai.
8000k H.I.D's for low beams and fogs