Climbing Pike's Peak

Like as previously mentioned, Pikes Peak toll road has been completely paved as of last two years. Anything will make it up, It is the coming down you gotta watch. They have a guy that takes an IR reading on your brakes on the way down. If your brakes are too hot, you have got to park it for awhile.
I live 5 miles from the bottom of PPTR and am pretty familiar with it. If you go out to the Continental Divide there are steeper and narower roads crossing passes at 11,000 and 12,000 feet that will really test you.

I towed my TT up the east side of the Sierras in my F-150 with a 300 C/I six without much trouble. I tried it with the same TT and a 7.3 Diesel and it was really struggling toward the top. Diesels don't like thin air and a Turbo really helps.

Be aware that some do get altitude sickness at that elevation.

The key to dealing with altitude is having a turbocharger on the engine. Without one; count on your power being down 40-60%.

In June of 1978, I drove my 1976 22 foot Class C up Pikes Peak. It had the Ford 302 cu inch, 2 barrel carb. I had my doubts that I could make it to the top, but the guy that took my entrance fee assured me that I could make it.
Started off OK, but was soon down to 5mph or less in low gear. I knew that if I had to stop that I could never get started again. I was a nervous wreck, but never let my wife know of my concern.
With a great sigh of relief, we made it to the top.
It was only after we got off the mountain, I told her of my concerns.
Pictures

I haven't gone that high, but I don't think I'd have any issues with the current rig. Where are the pics? :)

Pike's Peak is actually pretty easy. The road is really pretty wide. Lots of worse limbs in Colorado. Our dually and camper have no trouble with it at all.

What condition is the road in this time of year? is it kept plowed end to end year round for the tourists?

Big difference between a 68-72 GMC and a 1977 350 V8. The six cylinder, most likely a 250 cu in, had gobs of torque and was "free flowing"...no emissions (pollution pump back in the day) to get in the way. They were also geared for pulling....great engines.

The 350, by 1977, was detuned, derated, and would wheeze its way along a flat highway. They were rated about 140, maybe 150 hp. On top of that, they had short duration camshafts, not allowing them to breathe. GM (and others) had not figured out emissions on engines yet.

Your '13 GMC Diesel shouldn't hesitate a bit...but it will work up a sweat going up Pikes Peak!

Its 14,115 feet at the summit and it is now fully paved to the top. However, it is very steep with lotsa tight turns. Good luck, and I hope you make it. Post pix.