Same issue here on 2007 Tahoe 5.3 LMG motor. Cylinder 7 but on mine the lifters were ticking for almost 2 years off and on. Then on highway it stopped ticking and started missing real bad. I changed plug and wires and coil then did fuel injector. Nothing really helped and its smoking after running for 5 or so minutes and smells like fuel real bad in exhaust.