Welcome, I am Chris (aka-Moose)
The possible causes for brake fade are: There is still air in the system, a poor quality master cylinder was used, the rear drums brakes are not adjusted correct, during the MC swap air got into the the ABS which requires a scan tool to bleed out.
Verify the rear brakes are adjusted correct. Do 3 panic stops from 50 mph. Re bleed the brakes. Sometimes the panic stops will purge air out of the ABS.
----------Once you get an answer----------
1) Please realize I base my info requests and answers on what you type.
2) The more you can tell me the faster and better I can help.
3) I am not an employee for Just Answer, they pay me nothing to help you.
4) I am paid by the customer from your deposit, but only when you rate my answer.
5) You will notice it says rate to finish, rating does not close the post, or end our conversation.
6) I am going to stay in contact with you until you respond and tell me your happy or pleased with the answer. So please reply and let me know the progress on the issue and our discussion or if more help is needed.