Thanks 4crawler, but unless I am missing something on your website, I already adressed that particular problem. Like I mentioned in my original post, I ordered one of those thermostats you mention on your website from the local Toyota dealer (which took almost a week to get), and after installing it, I am still having the same problem. My biggest concern is the fact that I have never had this problem before. I have been driving the truck for almost 10 years in all sorts of weather (with the heater on and off) and have never had this occur. The t-stat I had in there until yesterday was in the truck for about a year with no problems at all.

By the way, you have a great website with a lot of useful info.

I bought a aftermarket guage today, I wouldn't call it mechanical as it is completly electrical(all of them in the store were fully electrical), and will install it tomorrow. Of course this brings me to another question. Since this aftermarket guage does not have a redline, at what temperature should I be concerned about overheating?