Your problem is for sure electrical. you will need to get underneath your truck if equiped with (electric switch in cab) and pull the plug off the t-case and clean it even if you have manual shifter chech underneath near the linkage. after that if that does not work you will need to pull the electric switch out of dash and check it. if nothing there i would replace the switch. be more than happy to help the best i can e-nail is
matt@texascci.com