.2 TPMS seems pretty decent - within 1/2 lb or so of my digital guage, analog gauges, and the one on the air compressor (the whole thing was $50 including the guage!). I use the digital guage though for trimming the fill after I get close with the compressor guage. TPMS is usually happy with that.

 

Assuming you are taking both readings with the tires cold, the variance you're seeing is a little high based on my experience. My system reads very close to the actual readings, within a lb or 2, I get for cold tires from three different gauges. When the tires are warm however, the cold/warm pressure differences you state are nearly identical to mine. I don't rely on TPMS to insure my tires are accurately inflated but I do check the TPMS reading regularly for any abnormally low reading which would indicate a potential problem.