I owe 50k thousand on a 5.375% mortgage payoff is 2019. I would like to pay it off. What is the best way to do this.

With such a short amount of remaining time, I'd suggest simply making bigger payments. Refinancing to obtain a lower rate might be worthwhile... for example take out a 5/1 ARM to get a rate of around 3.50%... then calculating what payments would be needed to pay off in 5-years or less. You need to factor in closing costs too... which is where the issues of cost vs benefit comes in, and why I suggest simply making bigger payments on the existing loan.

If you can afford to make more than the regular payment, you should do so. Any extra will go directly to reducing the principle. It is conceivable, however, with the same monthly payment to pay your loan off in less than 5 years. To determine this, more info is needed. What was your original loan amount and what is your current payment? With this info I can give you some viable alternatives.