The 5.3 isn't bad, and you probably won't know what you are missing...but the 6.2 definitely changes the driving experience...for the better. I have a friend that has a Sierra pickup w/ the 5.3 and the 10 speed. It's not bad...and is also about 800 lbs lighter that the Yukon XL I drive. But, I'd take my 6.2 for smiles per mile over it...If your order hasn't been accepted yet, you could go back to your dealer and have it changed...it is likely that eventually he will get an allocation for a 6.2. Meantime, if you want to drive both engine choices, or even all 3, including the diesel, the Pickups are pretty plentiful right now, go drive them all...then make your call. Performance will be very similar between them.