1031 Exchange to Rental to Personal to Sale. What is taxable ?

[Art Webb]

Hello,  I’m looking to sell a rental property and exchange into another rental property in a future retirement city.  After renting the replacement property for two years live in it as personal residence for 3-5 years and then sell it.  What are my tax obligations upon sale after living in the new rental property ?  With the Section 121 qualified vs nonqualified use provisions does my gain start with the replacement property’s net purchase price going forward or does it reach back to the prior relinquished property cost basis ?  Thank you for all responses !   Art