Replacing an engine is always cheaper than a new truck, even used one. If your brother is a mechanic, you can do it in your driveway. I am not a mechanic but with a help of a friend who is, I replaced a motor in my 06 Explorer (4.6 v8 3 valve) with a used one with 50k miles on it. It cost me $ 1600 including shipping, and 10 hrs on a sunny Saturday last year. I have over 20k miles on my "new" motor. Your 5.3 is so common you can find plenty of them. Also, your Avy has much more room in the engine bay, the v8 in the Explorer is a tight fit, but I recall my old Tahoe and there was plenty of room and easy access.
