You didn't bleed it wrong, that's correct procedure. 12 wides are putting a bit more load on the power steering than stock sized tires, being harder to turn the wheel at a stop is going to be harder for the truck. Are you checking steering with your foot on the brake? Because that will be putting more load on the pump, and basically taking pressure from the pump for the brake booster.
Where is the hissing noise coming from? Without hearing it, I can't say its normal. But it could be just the pump.
If you don't try to push the pedal to the floor, and just drive the truck normally, do you have brakes? Does the truck stop normally? Does the truck steer normally when driving? If you can answer yes to these questions, you're probably chasing an issue that is not really an issue.
If the pedal doesn't sink to the floor with the truck not running, it would rule out leaks in the master, ABS HCU, calipers etc.