still seems electrical to me. if it reads 260 and it's not blowing up then there's something wrong with the gauge or you have the best motor ever built. randomly stuttering at 55 could be anything really, most likely just dirt buildup unless it's really pronounced. in which it could be an 02 sensor. but that wouldn't have anything to do with a thermostat or ac/heat. your ac could be a bad compressor, check to see if the hoses are hard and i've heard that means the compressor or the refridgerant needs attention. i wish i could help more, but i haven't done much of this odd maintenance either
