I have a 1995 gmc 1500 with a 305 v8 with only 80000 miles on it and when I start it in the morning it idles at about 1500 and doesn't come down till I drive it for about 15 minutes and then it runs good at about 500 Rpms and it shifts higher too when I drive it for about 15 minutes then that comes back too normal too I tried changing the temperature sensor and no different and when I put the heater too defrost only I find it revs the engine up a little too can anyone help me thanks