Well, For comparson I had 6V53T in a 10,000 lb overgrown "1 ton" truck, and it had same tire size and same 3.73 axle gears, but it had the advantage of an overdrive 10 speed.
After several thousand miles of both loaded and empty from Virginia to Colorado to Washington state and back I'm sure it would have liked 3.54 gears, and would have them now if I'd kept the truck.

This GMC has less HP, ~170 not ~300, and is slower geared because no OD, those two factors should essentially cancel out and might be a perfect setup. But from my previous experience in a very similar truck I think it'll be close and if anything it might need a step higher.
I'm sure it'll be OK loaded, that overgrown F350 pulled and towed nicely in direct, which is the same setup as this GMC other than a little more HP. I fear when empty the GMC with 3.73 gears and no OD will feel gear bound and not be so comfortable on long trips on the highway, time will tell.

Grigg