I have a 1996 Dodge Grand Caravan LE. After it is driven for a while it will start loosing power and chugging. Transmission will start down shifting too. If you leave it for a few hours then it will start back up and go. Engine machine said it had a code for a vapor lock. It did this last summer but only a couple of times and when it was a very hot day but now it doesn't matter. Any suggestions?