I've been riding a 1992 Giant Iguana for the past couple of decades. A couple of years ago I put heavy-duty tubes in my tires and they held air pressure well. They were 1 1/2" tires and I kept them at about 50lbs psi.

Last month I rolled my bike and banged it up a bit, so I bought a new one: A Giant Escape 2, with Giant S-X3, 700x32 tires. These are narrower tires than my old bike. The shop says to keep them at about 70psi, and I've been trying, but every time I ride I lose about 10lbs of pressure in the back, and up to 5lbs pressure in the front.

Note - I'm a big dude: 6'2" & 310lbs.

I'm mostly riding bike paths/streets, with some grass and crushed-rock trails mixed in.

TL;DR: Big guy with new bike/narrower tires is losing air pressure every ride.

Question: Do I need to upgrade my tubes to something better suited to a heavy rider? If so, any recommendations?