It'd be interesting to see an image of you on your bike with a closeup of the tire/road. An image of your wheel where the joint is might also help.

Pinche flats should not be happening and that they are indicates either a underinflated tire or a rim problem. When I mentioned the rim joint upthread I was wondering if the joint was expanding slightly under load and thus pinching the tube. Btw, a pinch flat will not usually have a cut or even holed tire.

Next time you get a flat, carefully remove the tube from the tire but with the tire still on the rim. look for the hole in the tube and then look at the tire and the rim in that same area to see if you can spot what caused the flat. Doing that with a couple of flats should eliminate a rim problem if the flats are in different locations.

Hmm, I wonder if you have a spoke that's a bit too long and that pushes through the tube when the tire hits a curb or crack in the road?

Cheers

Read what it says on the sidewall. There should be a minimum, and you have already stated the maximum. Don't go over the maximum and stay above the minimum. You shouldn't need to be at the maximum, going over is asking for trouble, like increased flats and a harsh ride.

On my old Continental City Contacts, they maxed out at 65 psi, I usually ran them around 50-60. They were 26x1.5, 1.5 is 38mm. I now have Marathons on the bike, 26x1.5. They call for 55-100 PSI, I have the rear at 65 and the front at 65 at the moment. I have had no issues with a bike/load total weight of 82 pounds and me at 165. I think you would be much better off with lower pressures. Whoever told you that at the LBS may just want to continue selling you tubes and service.