Considering the high interest rate, the projects and COC return seems too good to be true.

I owe $40K on the loan & it has a high adjustable rate of 10.5% & rising ( started out at 8%).What I'm wondering is if I should sell or keep the property.

Consulting a real estate attorney is highly recommended, especially for complex transactions or if the standard forms need modifications.

I've performed all due diligence related to property. 

I highly doubt he is building homes in Texas from his self imposed exile to Portugal to excape massive litigation that was/is coming his way.He is a marketing guy and receives a commission for referring you to the builder developer who actually owns the properties.. at least that was his SOP in the past. 

With Amex Business credit cards, you can get 0% interest for up to a year, 2% cash back, and a welcome offer plus high credit limits without affecting your personal credit utilization.

I put in a little work developing a high level scope of work, assigning values and 3 resulting estimates so that I can not only determine what I think it will cost but what the best and worst case scenarios likely are.

But the stress of worrying about real estate assets and their performance is not what reitrement should be about.

You said highly leveraged but how leveraged is that?  

Dive into detailed market research, establish clear investment objectives, evaluate your financial readiness, analyze properties thoroughly, and perform due diligence before finalizing any transactions.