Making an old truck feel new

[GMC Guy]

Hey guys, so I just completed a long overdue LS swap on the ol' 74, plus a bunch of other small things I've been wanting to do. So far I'm satisfied and would never go back to an old school small block and three speed trans.

Now that it's back on the road and I'm driving it around, I've noticed that there are a lot of aspects to my 06 duramax that i wish were present on the 74, especially since the intent is to use it as a second vehicle. Cab noise, steering feel, and overall ride comfort.

Most notably, is the interior noises. The cab is undercoated inside and out, and mostly covered in FatMat, but i still have the rattles, squeaks, etc going on, mainly in the dash area.
I replaced all the weather stripping and had the vents rebuilt by Precision, but i still have quite a bit of wind noise and a REAL bad whistle through the passenger side vent... not happy at all after spending good money to have them rebuilt.

Moving on to steering feel. Everything is new (minus the box), and aligned. but the truck still likes to wonder around a bit... I'm thinking of upgrading to a CPP steering box.

Ride quality. shocks, springs, drop spindles, tires, everything is new. But for some reason my leveled 2500HD rides smoother? I really don't want to go air ride or coilovers for cost reasons, but now kinda regret it.

Any unwarranted noises drive me NUTS.. So i'm curious what you guys have done, or had to do, to make these squares feel newer. I'm tempted to gut the interior again, and start from scratch, insulating every piece.