OK - I thought this was a pretty simple request so I left a lot out of the story. Let me do a restart!
First - I live south of Denver in the Colorado foothills at 6627' so I fight serious hp loss due to the altitude. At 425 hp I lose ~85 hp, and at 500 I'm losing 100 hp. So I can do all the mods that you guys are doing and loving and I don't have anywhere near the same results.
I had my heads ported, larger valves installed, and milled them a bit for compression - maybe not needed as much down in the lowlands but highly recommended by my high country tuner to allow me to move more of this thin air. He also recommends I run long tubes to keep that additional air moving through.
I had the truck tuned on the dyno recently with the 6.0, hooker cast headers, BTR Stage 3 cam and the head work. It came in at a corrected 328hp at the wheels. That means take 20% off for altitude to uncorrect it and it drops to 262 hp to the wheels. With my 4L80e and 9” rear my tuner says I lose ~23 from motor hp to the wheels so taking that into account I’m back up to ~325hp at the motor.
According to BTR a stock 5.3 with long tube headers and the same cam should yield about 410hp. Take away my altitude hit and it’s about right. See their dyno chart. If you compare our dyno charts I am also dying off above 4500 RPM.
PS – one more piece of interesting info is this Richard Holdener test video
https://www.youtube.com/watch?v=5HL_VSFDEVg&t=20s on a 6.0 with a BTR Stage 3 truck cam (same motor/same cam as I have) with stock manifolds vs long tube headers. The results showed a big, fat pop in power lower in the RPM range. Holdener attributes it to the scavenging effect of the headers.
All of that means I am down on power and I am looking for ways to get a little more. Since the tuner, the dyno operator, Holdener and BTR all recommend headers I’m looking at them. However, I’m definitely open to ideas – how do I put some more power in this turd w/o breaking the bank?