Please Help. We're working on a 2001 Chevy Silverado 2500HD.It was stuck in limp mode. We first got the P0783-85 codes, so we replaced both shift solenoids, as well as the wiring harness. Still shot the same codes and was stuck in limp mode. So we replaced the transmission. Still didn't work. Now it's pulling up P1860 and both shift solenoid again. Also I realized it was shooting these codes before I even put it in gear. And that's what makes me think it's the ignition switch. Any help at all will be greatly appreciated and save my sanity.