[SgtBob]

I’m a pilot...I’m frequently in contact with FW, HU, ME, KC, AU, and ID.

I do have a close friend, who works FW. Known him and his family since ‘73. I don’t understand what knowing someone in ARTCC has to do with anything...

[Yosemitest]

Your friend at FW should have explained it to you, reference comment #170

and their use of the Standard 29.92 altimeter,
how that affects the Mode C readout of the aircraft's altitude,
and where the data FlightAware gets comes from on the Flight Track Log for UPS1354.

It comes from the data received from that aircraft's mode C.
And based on what's on that Flight Track Log, the data was not continuously transmitted twice a minute.
Sometimes it was received only once a minute. or not a all for over a minute ( 05:33-05:40 ).
Could that spotty reception have been because of the weather?