when the factory warranty expired on the denali, we bought the one they sell at the dealership - many people find this to be a waste of money (including my parents) - let me tell you a story............
we bought this car new in 06 - before taking delivery it got 22x10 wheels with 305/40s on them, big sway bars, big rear springs, lowering, and monstrous brakes - shortly thereafter it got a volant intake, throttle body spacer and reprogramming - we have put a LOT of miles on it (about 55k now) - we have dragged it across country a few times, trailer right behind it - we haul stuff everywhere - this car gets a lot of use, we knew it when we bought it, and did everything we could think of to make sure it was trouble free and up to the task
the car has not been without issue though
it was in an accident which banged up the front end, and required new front right suspension work - it blew the tranny (twice) - it has been in for a number of small things (noises, squeaks, steering shafts, etc) - all in all though, it has still been a great car, and we love it
i have been dilligent about keeping the car running right though, and take it in regularly - i also run the best fluids i can, and don't let things go - i even had the tranny serviced early as a preventative measure - just before the factory warranty expired at 36k, we purchased the one they sold - costs us about $1000 a year - that may seem high, as most people don't spend that on repairs, and it doesn't cover stuff like oil changes and regular services and such
a little over a week ago, after taking it in to have all the differential stuff serviced (not covered), and to have a clicking noise diagnosed, they found the front diff to be toast - they rebuilt it (twice) - all covered - however, same noise - back in it went - it took them a week to figure it out, but it turns out i smoked the transfer case - $3800 - totally covered
that warranty has now paid for itself 4 times over