Is the suspension on your 2008 original from factory? How many miles on the truck?
The 5th gen is bigger and heavier and suspension components have been beefed up to reflect that. Without the ability of reading Toyota's mind, it may be that they tried to keep as soft as possible in a sea of crossovers to hide it's truck dna from potential buyers.
I have KDSS on mine and it feels busier and more taut than the SR5 rental I drove before it.
There are some threads out comparing the two suspensions, but they may not provide insight into what your "feeling" when comparing the two.