2010 doesn't bring anything significant to the table from what i've read. the 6.2 is great, drove a couple denali's with it, friend has an 08' pickup with it, changes the driving experience alot. Hit the gas and you're gone. If you can afford it do it, i would've, but i'm not spending another 4k on the truck for the bigger motor. all the 6.2's around here had EVERY option including the power running boards, which i don't like at all, I like mine in place to protect the sides from chipping (big issue i had with my TBSS). But at the price point of the 6.2's, from what i've seen, it's just about worth getting a denali ,interior is nicer and the resale even that much better you know? Unless the AWD v 4WD is a problem for you. I like the look of the tahoe better, but i would take a denali any idea if the price were the same for the interior. good luck and yes there are no more 6.2 tahoes being made, rare? yeah, but i highly doubt it will make you anything extra on a trade, or sale of the truck besides the difference in price from a 5.3 when purchased. Drive them both. be careful though the 6.2's power is like "Crack" to us car guys lol
ps i did hear variable valve timing is coming for the 5.3, that would be important. even though the output may not be significantly increased you will feel it while passing people.