Our 2006 Chrysler Pacifica idles great, runs great on the highway. At speeds of 20-50km/h the car surges, feels like the car cant decide what RPM to be at. I tested today at 30 km/h, held the accelrator at a cruising rpm and the rpm would go from about 1200 rpm to 800 rpm and almos stall. Once again this only happens at below 50km/h and seems worse the slower you go. Could this be a transmission speed sensor? I have check and there is no codes in the system and no engine light has ever came on.