TPMS shows different pressure than pressure gauge

I have a TST TPMS w/ 10 sensors and the never read the same as the tire actual Tire pressure gage. That's OK as long as they always read about the same when tires are cool in the AM. I have one tire extender that causes a loss of about 1psi a month. Very aggravating to have to deal w/ this problem. I just recently bought new tires and that tire was flat the next day in storage. This is my 2nd TPMS system. I'm very frustrated w/ TPMS systems & am considering to eliminate it altogether.