My 2016 Tahoe's lift gate was acting up and took it to the dealer for a fix. Over the last few months they have changed out the lift gate actuator, module, struts, and latch, rear fuse block, and both battery positive cables. Fortunately I bought an extended warranty with the Tahoe and this hasn't cost me anything. However, the lift gate still does not work properly. The dealer even consulted a GM engineer on this. Everyone is stumped. Any ideas?