265 tires on GM stock wheels

have any of you had any trouble using your larger tires on the narrow (6.5") GM wheels?

Twice.
Both times I bought a used truck that someone had put 265 tires on those small narrow wheels.

Bad idea for a load carrying vehicle such as a pickup carrying heavy loads such as my 9' 6" truck camper and especially with heavy GN trailers.
The tires need max pressures at these weights which both times caused the tires to ride on the centers causing handling issues. If your not carrying heavy loads then the mis match tire/wheel width may work out for you.

The truck with the TC wallowed all over the road.
Heavy GN trailers pushed back of the other truck around to the point I was using trailer brakes only .

I bought the correct 8" wheels for the truck camper combo. No more handling issues.

For the truck/GN trailer I went with the narrow 235/85 E tire. Tracked like a sled on rails in all situations.

If your carrying max axle (6000-6200 rawr) loads the 245/75 E may not have enough reserve capacity.
Most of the 6.5" GM wheels aren't rated but around 3100-3200 lbs.