2006 chev, express van 1500, 4.3 V-6, auto. My shifter has 1st 2nd 3rd and drive. First and second are perfect. When it shifts to 3rd there is nothing and drive is the same, nothing. This happened suddenly, one-second good, next second, no 3rd or D. I hear there are fuses and sensors that can cause this problem. Thanks in advance for any advice. tom