First off I know this reply is the same as talking to myself, but my success in this repair might help other 1999-2000 Ford F53 chassis owners who do a internet search for these error codes P0720 and P0500 . I have 1500 miles after the fix and no more error codes or shifting problems.
Ford had a ground harness update but it has been discontinued and is no longer available. I guess most of the chassis that suffered from these problems were repaired under warranty. My chassis started showing the shifting problems and speed sensor error codes intermittently at 13 years old and 60K miles.
The repair: I located the 7 ground wires on the main PCM connector as described in TSB-02-11-3 and cut them 6" from the connector. The wires coming from the connector were spliced to one conductor and terminated with a ring connector bolted to a clean ground on the firewall. The remaining cut wires that disappear into the wiring harness were taped back and abandoned.