Not true about dash rattle. Both my trucks with the older interior rattle. It’s just the gauge bezel cover but still annoying.
Both have highs and lows. You like the look of the Kim and don’t mind dealing with more emissions? Go for it. In the end it’s up to you.
You can fix that rattle in less than 5 minutes though. The LMM needs the entire upper dash replaced eventually if not parked under cover.
I don't think the seats really sucked till 2011 trucks when they are all squared off like ford seats.
Head gaskets on the early 06 can still have problems but really all years can.