So the van is new to me. 100K miles on a 4.8L V8. Hooked up my 12' cargo trailer with electric brakes. Pulled fine until I engaged the tow/haul mode. Then it wouldn't shift from 2nd up to any gear. I tried disengaging the tow/haul button, and the light went off on the dash, but still stayed in 2nd. I couldn't shift manually UP. I didn't try going down, as I was on the freeway, and first gear wasn't ideal. I pulled over and unplugged the trailer. Turned off the van and restarted it. It then shifted fine with the tow/haul utton NOT pushed, but the engine light is now on. I initially thought it might be wired wrong with the aftermarket brake controller, but that wouldn't effect the shifting. So my thoughts are in the button. I don't know what the code is yet...but I'm gonna find out. Any ideas?

 

I've seen this issue pop up on a few newer Silverados, seems like a software glitch so try disabling and re-enabling trailer towing in the truck's settings menu, that usually fixes it.

 

I've seen that Tow/Haul button issue pop up on a few newer Silverados, where it seems to get stuck on or the truck refuses to engage the mode. It might be worth checking your battery terminals and making sure your fuses are good, especially if it's happened after an update or upgrade to your infotainment system.