You failed to mention what you are towing and what terain you will cover. The blazer even with the small engine would be fine in say, the south west. The F-150 could even have trouble in the rockies. Terain is a big factor to consider. Personally I would get a U-haul dolly and jump in the Ford. I'm partial of course, I wouldn't trust the Blazer to haul my groceries. If the F-150 is old and high miles then you might as well give it one good last haul, then do a drivetrain build, although I don't think you will need it.
