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

Mar 14, 2023
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.