New York (CNN Business)A nasty surprise awaits the 34 million drivers expected to hit US roads this Memorial Day weekend — the highest gas prices in seven years. And that could be the least of the problems for the those taking to the highways for summer vacations. The gas shortages experienced earlier this month when a key pipeline shut down could once again be on the horizon, according to experts. This time, the squeeze could be triggered by the lack of tank truck drivers to deliver the fuel, and a repeat of panic buying by travelers topping off their tanks."I...