Finally, some relief at the pump: the cost of a gallon of gas in New Jersey has begun to drop from an all-time high of $5 a gallon set early last month, with some counties seeing as big as an 8.5% decrease. The average cost of a gallon of regular gas was $4.638 on Friday, July 15. That’s down 38 cents since June 7, when the statewide average broke $5 for the first time ever. Every single county has seen a decline of more than 6%, but some counties are feeling more relief than others. Bergen, Sussex and Union counties have seen their prices drop more than 8%, and Sussex also has the cheapest ga…