Auto Parts: 1988 toyota runs hot, head gasket failure, combustion gases

Question
I have a 1988 Toyota pickup with a 3.0 liter V-6.It just recently began to run hot almost to the red but not quiet. It used to run below the half way point on the temp. gauge. I replaced the thermostat (180 degrees). I replaced the upper and lower hoses. I also purged the system of air(left running for 20 minutes with cap off.) I can see fluid flowing in radiator. The radiator seems to be stock, but fluid looked clean when i drained it out. I live outside of Houston Texas. I only use vehicle for offroad use only in four wheel drive usually in low range.

Answer
    There could be additional air in the system that won't reach the radiator at idle.  Driving the vehicle for short stretches and letting it cool off should get that out.  These older V6s had aluminum heads and iron blocks.  This results in the two expanding at different rates and eventually causes head gasket failure.  You can test for head gasket failure with a test strip that you buy at a parts store.  If combustion gases are getting into the coolant the strip will change color.  If this is the case you should change the gaskets immediately.  If the engine actually overheats (goes into the red on the gauge) it will warp the heads and they will have to machined or replaced.  This will also allow you to peek inside the block and see if there's a lot of crud in there.  If there is, you will want to clean it out.  The only special tool needed will be a torque wrench.  Replace the cam belt and tensioners while you're at it.