Before this thread goes totally haywire....
Yes oil patch truck likely had many thousands of hours on it even with low miles. Our trucks on the slope were averaging 2000-6000 engine hours a year if they'd been used all year, we were only running them for about 6 months a year.
Alberta patch likely a bit less hours vs miles because those trucks do get driven down the highway sometimes but still very high hours.
Yes the 6.0 has noticeably less power (torque) but the 6 speed trans will help with that compared to the 5? speed in your deceased Ford.
Had a lot of 6.0 Chevys and V10 fords in the fleet running them back to back in Colorado mountains. The Fords pulled better, but the Chevys always made it to work as well.
No, you're not going to hurt it keeping your right foot mashed to the carpet up the Coq or any other pass.
And the newer GM will be a bit smoother and more comfortable.
Enjoy!