2004 Dodge Caravan SHIFTING WHEN IT SHOULDN'T

WHILE DRIVING AT A CONSTANT SPEED BETWEEN 45-55MPH (MY 40 MINUTE COMMUTE DAILY) THE TRANSMISSION WILL TRY TO SHIFT UP(REV UP) OR DOWN WHEN IT DOESN'T NEED TO. THIS SEEMS WORSE WHEN IT'S COOLER OUTSIDE AND DOESN'T HAPPEN ALL THE TIME. WHEN IT IS ACTING UP IT IDLES ROUGH AND SEEMS LIKE IT MIGHT STALL WHEN IDLING ALONG IN SLOW TRAFFIC. FINALLY, IT WILL ALSO HAVE DIFFICULTY WHEN ACCELERATING. AT 20MPH WHEN IT SHOULD SHIFT TO NEXT GEAR. IT WON'T. SOUNDS LIKE IT'S WOUND UP LIKE A TOP. COULD BAD GAS OR ETHANOL BE CAUSING THIS? WHAT DO YOU SUGGEST. IT'S BEEN TO THE DEALER TWICE, OF COURSE IT DOESN'T ACT UP WHEN IT'S THERE.