Temporary, removable stake extensions would give you the best set of options; the most versatility for your bed. You'll be tarping your load for the trip, I expect. Get a bunch of those little hooks to retain the tarp (bungee) straps and put 'em 12-16" apart, low on the sides. If you think the thermostat needs changing, then it does. An oil change would come right after that on my truck, because an engine which hasn't run hot enough has put a lot of what you don't want into your oil. Once that's done, take another look at your gauges. Then if you don't like what you're lookin' at, go with what Tomcoe said. All these things are cheap insurance.
The brakes are another thing. What makes you think they need work?
