I'm not sure where you are running your numbers through, but 140,000 at 4.25 is 688.72. That's not even factoring in the guarantee fee, or your taxes and insurance.
Also keep in mind that your preapproval is either an estimate of PITI or a maximum PITI that you are approved for. It can never be an exact figure since it has no idea how much your taxes are, how much your insurance will be, or what the rates will be when you lock (they have gone up dramatically over the past week...if you are looking for 4.25, you are going to be paying up front for it right now).
I also want to caution you against USAA for your mortgage. For banking, they are great. For insurance, they are excellent. I actually refer a lot of my veterans to USAA for their insurance quotes because they are the lowest around. For a mortgage, their customer service is terrible. You do not speak with a licensed loan officer. You get pushed off to a processor who will not return your phone calls. You upload your documents and hope for the best. The documents get lost and your closing does not happen on time. That's exactly what happens when you go with a company rather than a loan officer. I personally closed 2 VA loans last month with borrowers who started with USAA. And that's just me.
USAA does so many great things for our vets. Closing loans just isn't one of them.
Mortgage banker for 15 years. We lend in 49 states.
Concentrate on government loans - FHA / VA / USDA and first time home buyers.
There is still 100% financing available in some areas and I can help you get preapproved!
Real estate paralegal for 10 years prior to working in mortgages.