I feel that I am about to find out why my truck was so cheap: I just bought an '05 with the I5, and knew about the head issues going in but understood they generally only affected low-miles engines (mine has 147K). Clean Carfax, it was a lease vehicle until 2008 so all its services during that period were documented. ~250 or so miles into ownership, it threw a check engine light and is posting the dreaded codes P300 and P304 (random misfire and Cyl 4 misfire), along with some other stuff (PO128 for the thermostat, U1026 T-case communication, PO455 Evap/Emission system leak). My question is, CAN the head issue manifest at such a venerable mileage? And if the head is deemed defective, will GM do the TSB-related work at their expense, or does it cost money? If the latter, does anyone who's been through this know approximately how much it costs (say in the worst-case scenario, if it needed the head replaced)? Please forgive as I haven't read through the whole thread yet. Working my way through it in scraps of time at work, any feedback in the meantime would be appreciated.
I can't say for sure in your case but my understanding is you're probably beyond the qualifying mileage for GM to cover the cost of the replacement head ....(if that would resolve the problem(s) you're having).
In my case the head was replaced at 6700 miles under warranty. I have 114k miles on the truck now and it's in having another head replacement, this time on my dime. The truck is still at the dealer but the estimate they quoted me for replacing the head is $2859.
It's a lot of money to spend, in my case, on a 10 year old vehicle and there's no telling how long this head will last. I've taken good care of the truck over the years and a new one is 10x the price of a new head.... so fingers and toes.... Good luck.