I think you gotta take the capital gains hit on rental property and cannot roll it to another like you can with a residence. As with any other investment, the cap gains is a real and valid form of "income" and is taxed accordingly.
The good part is that the cap gains rates are fairly "civil".
Now, your RESIDENCE (amd maybe even your second residence) qualifies for a "reinvestment period" where the gains are not taxed if reinvested into another residence.
ALSO you get a ONE TIME exemption from gains tax on a residential sale (up to 1/2 Million in gains).
As always, be sure to check with your tax advisor.
(but I am not familiar with a rollover for rental property).
If one exists, I'd like to know (I've got a piece that I'm gonna sell to the current renters and It'd be great to be able to roll the gains into a new one _I already got my eye on the rpelacement)