@Steve Manoa thank you for providing details. If you sell now you will get about $370k tax free, so we should calculate the return you will get on that money (Return on Equity). The return will be made up of cash flow, principle paydown, tax savings, and appreciation.
Rent at $6400 minus expenses for vacancy 4%, cap Ex 4%, maintenance/repairs 4%, and property management 8%; you said it's new, rents easily with great tenants and has a maintenance payment built in so let cut this back and say 15% of rent instead of 20%. That means cash flow wise it will lose $250/month, so negative $3k per year.
Based on some assumptions I made about your mortgage, the principle paydown should be about $2k/month, so $24k per year.
Tax savings you will be able to deduct the entire payment $5700 minus the principle paydown $2000 plus expenses $950, this equals $4650/month, so $56k plus depreciation (assume 90% improvement value on $1.2M basis /27,5 years) $39k, with rental income of $77k this equals a loss of $18k per year against your income, so lets call that $10k value.
So far we are at $31k on $370k is an 8% return. plus appreciation of maybe 2%, so $24k, that brings us to a total of $55k which is a 15% return. I'd keep it as rental, but only do a 12 month lease at a time because you want to re-calculate in 2 years to see if doing the IRS section 121 exclusion is worth it or not, you really don't have much of a gain, but I'd still want to do the math especially since the rate adjusts at that point too and if you do decide to sell in 2 years you will want it to be vacant when you list it.
Build up your emergency fund, but DO NOT pay extra towards the principle, you can make a better return and keep your money more liquid by investing in pretty much anything other than additional principle payments.
As far as borrowing money for a rehab just compare rates, unless you are tight on cash flow then consider the HELOC as that will likely be a higher rate, but interest only payments during the draw period.
I hope this helps. Good Luck!