If the shift motor was seized then the bike should be at least tried with a known good shift motor ... The ECM thinks the maximum time needed for the shift dogs to make full engagement is 34 milliseconds , but will continue to rotate the shift spindle for 70 milliseconds.. It is possible the ECM is damaged if it was tring to rotate a seized motor to many times ..
There are homemade tools that can be used on 1998-01 (pre-code models) ..1 of them is the light bulb test in place of the shift motor...
Here is the info

The price of the ECM (on this model it is actually called "change control unit") this sells for $468.80 CDN ... Myself I would have a dealer do the tests on the ESP system .. If you look for a used ECM any TRX450ES 1998-01 is the same , but don't buy used without a guarantee..
There are homemade tools that can be used on 1998-01 (pre-code models) ..1 of them is the light bulb test in place of the shift motor...
Here is the info

The price of the ECM (on this model it is actually called "change control unit") this sells for $468.80 CDN ... Myself I would have a dealer do the tests on the ESP system .. If you look for a used ECM any TRX450ES 1998-01 is the same , but don't buy used without a guarantee..