Even if it means using two gallons of gas while waiting in lines at the border, a new trend of filling up your tank in Mexico is worth it for those who have SUVs and trucks. Regular gas costs $2.54 a gallon at Pemex stations in Tijuana compared to San Diego, where it's over one-dollar higher at $4.624. Then you've got diesel at $2.20 in Tijuana vs. $5.04 in San Diego. However, one problem does......