Burningman, I have no doubt that your truck can pull 23,000 combined up any of the local passes just fine. But to say that it's going to outperform the new trucks doing it, just shows that you've never towed with the latest generation trucks.
I've done both. I've heavily modified the older trucks to tow as well as the new ones, and towed with the new ones.
Sure, you might make it to the top of the pass just as quick as some of the new trucks towing 15k. But they aren't billowing a cloud of gray or even black smoke on the steep sections, and their drivers aren't having to do that delicate dance between their right foot, and the EGT guage while wearing earplugs. So no...don't think you'll be embarrassing any of the new trucks anytime soon.
So for your $40,000 build, plus the cost of your truck new at around $25,000? ....you spent $65,000 to get your truck to tow at 23k combined effectively.
I spent $62,000 on an F450 Platinum, that's rated for over 40k combined, that comes with better brakes, intergrated engine braking, integrated trailer brakes, better tow mirrors, traction control, trailer sway control, backup camera, better tires, and all with a factory warranty. See?... just two different ways to get the job done.
It's great that you love your old truck, and with all the mods you've made. I'm sure it works great for you. I've gone that route before with two previous trucks, a 1999.5 7.3 F350 CCLC 4x4 DRW 6sp and a 2003 F350 SRW CCLB 4x4. Both put down more HP and TQ at the wheels than my stock 2015 F450. But neither would tow anywhere near as nice as these new trucks.