FWIW, lots of talk about water in the brake fluid. Good stuff, but all brake fluids have a boiling point. Look at the can, the higher the boiling point, the more expensive. Ford had such bad dragging brakes they came out with their own brake fluid trying to defeat the problem.
Your shoes are dragging is the most responsible guess. You need to fix that issue an perform all the other brake maintenance items in the owners manual for extreme use.
I personally would not go any distance till I had the calipers cleaned/greased. More then likely the shop will just want to replace them since that’s what they know, unless you’re in a truck shop with old school mechanics.