Keep in mind you will be paying closing costs when you double close which normally eat up about 1k worth of profit (or a bit more).

After a while it starts eating away at me and making me depressed.

Now I eat the cost and use a good, licensed master plumber instead.  

Interesting on the 15 yr, because I technically don't live off my cash flows either, however I DO use those cash flows to acquire more, so I'd assume the 15 yr would eat away my cash flows so that I couldn't acquire as quickly.  

With it constantly eating cash for monthly mortgage payments, property management fees, turn over and repairs,  it may hurt your investment goals and will effect your mindset.  

They could quickly eat into that $7500 monthly profit.  

I have talked to others that says I can do zone with dampers no problem while I have talked to others and read online that doing this will be a maintenance nightmare and that I really am better off eating the cost and doing a split system.Has anyone else had a similar situation and re engineered hvac from split system to one larger system?  

That certainly could be cured by year end and we would expect the return to stabilize similar to the previous year as the variables shouldn't eat away more than they did prior year within a deviation or so.  

We are in our early 60s now, and would like to avoid having to eat cat food when we are 80+. 

In my case,  I have a 2/1 (living room, eat in kitchen, 2 beds and 1 bath) and is smaller, ( 800sf).