GPS satellite ECEF positions not aligning closely enough with TLE ITRF positions

Mar 14, 2023
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I'm not sure if this is the right place to put this but basically I'm parsing a gps message and calculating the satellite's ECEF coordinates from the parsed parameters. I have been attempting to do this and compare them with TLE ECEF positions but something is clearly wrong as they are very far off. I have been following this pdf : but it feels like I'm missing something, I am thinking it is a timing issue (i.e time calculations are wrong) or a rotation is required but I'm unsure.