one question, IS your runner a 3.0L? If so I had the exact same problem a few years ago on my 88', I did the exact same things you speak of here. Honestly, unless you see little floaties hanging out in the coolant when you take the cap off, i doubt its a blockage. I went through the same line of progression then. My guess is that its an air bubble in the system. It will cause your gauge to read funny and the engine to heat. The solution is that you have to "burp" the system. There are a couple ways to try this. The simplest is to leave the cap off and let the engine run at idle (sometimes i kind of repeatedly squeeze the upper hose to attempt to force air bubbles out). If that dosent work, I have taken the highest coolant hose you can find loose and run the engine till you get flow there (run with the heat on high always). Also find a way to have a catch vessel for the coolant run off (may have to couple a piece of heater hose on to it what ever). I had to use the second method to get mine to "burp", after that no more problems ever (coolant wise). Hope that helps, might be something to try before you spend any more money. These may not be the only ways to burp the system, I am not a mechanic so... maybe others will chime in with their method.
Good Luck - J
