My brothers got this 1995 Nissan Quest XE that he just drove from Dallas to Tampa. It runs fine when the van is moving on the road, but then he comes to a stop or has to idle, it over heats really fast, but when he takes off it returns to normal. It has new radiator and hoses that were installed just before he went on the road trip. He called the mechanic that did repairs on it just before departure and he seems to think its the thermostat. What do you guys think it is?