Go back to Costco and have them take their device and reset the tire pressure sensors. Have them check all 4 wheels. My story, this spring, I had 4 new tires and sensors installed on my 2007. I get home, and the TPMS light comes on. The tire store and I played with this for a few months. They would replace sensors, and after driving maybe 15 miles, the TPMS signal would return. They got updated software for their programmer. We played around with this a number of times. The dealership told me they would not work on aftermarket sensors, and I would have to get OEM sensors for them to work on it. FINALLY, the tire store found a reset program on line. They were to lower the tire pressure down enough until the sensors all showed low pressure. Then they would drive the van around at 35 mph for a short distance and time. Then they would correctly set the tire pressure and it was supposed to clear the TPMS alarm. It worked.
The tire sensors are powered by a coin battery, and it has a finite life, so when you get to the end of life on the battery, the sensor gets real flaky. The tire place has a RF transmitter/receiver/programmer that can talk to the sensor, so they should be able to tell if the sensor and its battery are good. The sensor and the receiver in the vehicle need to talk, and that is what the programmer and the driving the vehicle are supposed to establish. At least that is the way I understand it.
Good luck with it.

 

You'll have to go back - the programming didn't take.

Before I got my cloned sensors, I went through that crap twice a year - most of the time the reprogramming worked fine the first time but I had to return to the tire shop more than once so that the programming process could be restarted. It's a pain in the butt but it's not a big problem.