My Costco is fairly close to the Interstate, but no diesel pumps. I believe Costco has studied this issue concerning the pros and cons to offering diesel to customers. If customers would express their desire for diesel fuel, maybe Costco would consider adding diesel at their fuel station? Costco could add one diesel pump at each fuel station and see how things work out. The other thing is making sure customers know this is a diesel pump to prevent gasoline customers from pumping diesel into their gas vehicles. I've seen this happen before at other fuel stations. I've seen this happen once where a man was ready to fuel up his Toyota Corolla at the pump, although this was clearly a diesel island, the man almost pumped diesel into his Toyota Corolla. I was able to say something to him before he squeezed the nozzle, he was happy I saw this catastrophe before it happened.
As far as Top Tier Diesel Fuel, it would be great if more diesel brands would offer Top Tier Diesel.