I want to know what tubes you are using that only lose 1 to 2 psi per week, or per month? And what pressure are you running them at? I would say that 10% to 20% pressure loss per week off the maximum pressure is not unusual. So if I run my tires at 100 PSI, they could be down to 90 or even 80 PSI at the end of the week. Certainly still rideable, but it changes the ride. Past a certain point, the rate slows, but that point is pretty underinflated for my taste.