After alot more reading and debating I have decided to just leave the stock manifolds for now and just run a Jegs ORY with (2) Thunderbolt hi-flow cats added to it. That'll give me a upgrade over stock pipes to muffler at least. Wife requires cats after smelling my truck without, lol. I'm also gonna add a Thrush 17637 di/do muffler which I have on my truck and absolutely love the sound of. I'm debating leaving the stock single 3" tail pile which would require a y pipe transition immediately after the muffler or just buying the Walker tail pipe replacement and running it side by side with the stock one so both exit in the stock location.
I'll deal with replacing the manifolds with some Summit shorties when I do the 411 swap. Not worried about giving up top end with shorties as this Tahoe will be a basic daily driver and to tow with. I do wanna go with a GM 14097395 cam and stock LS6 springs as well. That seems like the perfect cam for a bump in stock power range without worrying about any clearance issues or TC upgrades either.