There appears to be a problem with the lifters in these 5.3L AFM engines that GM won't admit. At 87K miles and 5.5 years old GM garage says lifter is collapsed & wants to replace all 16 @ $3400 & @ my expense. There are lots of posts from drivers with this problem but GM won't admit and GM Customer Service is only lip service... "out of warranty sucks to be you". GM & the dealers don't care... take my advice and buy a Ford. I'm stuck with this piece of crap cause I just paid it off and can't afford to buy another $40,000 mistake. BTW: this AFM engine is the same as in current models... beware!
Very impressed with this vehicle. Sold my 175K mile Sierra and due to its excellent performance, I'm sold on GMC. The Denali drives and handles great. 18mpg hwy and 16.4 in town. Not bad for a 6.2 ltr V8. My previous 4.8 ltr V8 only beat that by 1mpg! My vehicle came loaded w/options and couldn't pass it up for $38.5K. With gas prices I think they are really having to come down on these things. Very quiet ride on the highway and around town. It does need more storage compartments/center console organizer. I would rather the center console open from the side rather than front. It's somewhat awkward and has a rather flimsy spring hinge.
Overall, i would not buy this truck again due to repair costs. At 104,000 miles (notice it's just outside the warranty) engine heads both cracked - with the mileage and the reported issues about oil usage and AFM related issue, it makes more sense to replace with a GM crate engine than to solve part of the problem. Mileage on E85 is 14mpg in 2wd if you are an extremely light footed driver. With 87 octane, the average mpg (light foot) is 18mpg-19mpg in hilly terrain. As a cowboy and rancher, my vehicle is my lifeblood and cost of ownership and reliability is key. This truck just hasn't met the minimum expectations. Cost for new engine at GM dealer - $7,898.77
Bought in July of 08, currently have 65K on the truck. the only gripe I really have about is a major one. The powertrain. I'm not a hard driver, mileage has been mostly highway. I've had the forward sprag gear brak in the transmission, a front wheel bearing start to come apart, and now its sitting in the service department for low oil pressure. It also is down 2.5 quarts of oil with 25% life left on the monitor and no low oil level indicator. I've been told by the service department that the engine can burn a quart every 1000 to 2000 miles and be considered normal. I've reviewed several forums on the issue, and there are alot of people with with the same issue, being told the same thing.
So I've had the truck less than a year. It has only 18k on it. I've had to replace two door lock switches. I've also replaced a leaky oil pan gasket. It's been in the dealership 3 times. When I wash it the door moldings leak for hours.