I currently own a 2008 Dodge Grand Caravan equipped with the 3.8 litre V6 and the six speed automatic transmission. It currently has 344,075 kilometres on the clock. Within the last month I have been having a bit of trouble with the transmission. I will be travelling at 50 km/h and I will hear a thump and the RPM's will go from 1500 to over 3500. I enter the 80 km/h zone and speed up and the RPM's go up to 4500. I will shut it down then it seems to re-cycle itself and will work flawlessly for some time then will do it again. It does this intermittently and will not occur for days at a time. I was slow on changing the transmission fluid and filter, did not do it until I had 224,000 kilometres on the odometer. Am I looking at a major repair or could it be something such as a sensor that might be easy to have repaired?