GMC Troubleshooting Questions? Ask a Mechanic for Answers
Does your truck have active fuel management?
a non working afm lifter does not make noise. I would pull the valve cover and bungee up your coil packs then start it up and watch the rockers on cyl 6 while watching the scan tool and see if they stop moving when the miss is occuring.
they stop or they don't? sorry i didn't understand what you mean.
if its electrical it would more likely be a bad connection or wire than an ecm. I would do a cylinder leak down test on it next. Once the is starts is is consistent like a dead hole or still very intermittent?