Toyota Repair: overheating 1996 tacoma v6, blown head gasket, smog test

Question
My 1996 Tacoma with 136,563 miles is now overheating with regularity when under load. Either towing from 1000-1500 lbs, or with the factory ac on. I have changed the thermostat and had the radiator flushed and checked. Still overheating. I have not had the timing belt nor the water pump changed yet. I have read some other of your answers and a blown head gasket seems likely. Would you agree and is there a test that i can do to see if either the head gasket or the water pump is bad?  

Answer
The headgasket can be checked for a leak by using either the block test method, a test fluid is used as a medium in a container which is attached to the radiator opening with the engine running, the fluid is blue but if there are any hydrocarbons in the coolant the fluid will turn green or yellow, the other method is to use a smog test machine which is much more reliable, the probe is held near the radiator opening with the engine running and the hydrocarbon reading is displayed on the computer screen.
I recommend doing this first to eliminate the headgasket as the possible cause.
If it turns out that the headgasket is not the cause replace the radiator, it may be clogged to a degree where the coolant circulation is not enough to cool the engine, the A/C is designed to turn off when the engine is overheating, once the engine overheating is repaired try restoring the a/c to it's original configuration.