Dual Rear Tire Valve Stems?

After doing all the research several months ago and deciding I needed the one piece valve stem and then calling around for someone to remove my tires to install them I went with a TPMS that has an in cab display. I still have to pop the hub caps to add air which is a pain but it is really nice to just flip the monitor on 5 min before I leave and read the tire pressure and temp of each tire. It is also very informative to see the temp and pressure change as you heat them up and one big surprise was watching the right hand side heat up and pressure rise going across SD with a strong wind from the left. In the 6 mos I have had them I only had to add air once because of the dropping temps and double check the monitor accuracy against my digital gauge.
They do all read 2 psi lower than my gauge but I am not sure which one is off since 2 psi is within the spec of both.