I dont know if Cosco will. 265 is the largest that Discount will install on PYO wheels. I got Nitto Terra's, They are still small but a little bigger than 245... no problems though.
Dont know about Costco, but I got 265's on my stock van wheels (came with 245's on a 3500)
Look and ride way better. Only problem I'm having is the garage door is 7 foot, the van is 7 foot, then I put on tires an inch taller. But that shouldnt be an issue with a truck.
I got E. I did not look because it's been raining a lot. When I can look underneath I'll let you know. There are some on the outsides though.
The ride is much better. Why didn't GM put these on from the factory? They certainly fill out the wheel wells better. I think the K3500 SRW comes with that size. Kat? Did Big Blue come with 265's?
I will take pictures when the rains subside. Yesterday we had like 8" in just a few hours.