Attention: TDR Forum Junkies 
When you are really into the turbo, like interstate towing, the heat is really absorbed pretty thoroughly into all the metal parts of the engine, especially the ex. manifold and the turbo. The reason it takes a while for things to cool is because the metal is really "soaked" with heat. (If you just do a quick run somewhere, you haven't really given things a chance to heat up yet). And remember, the temp of the air around the probe and the temp of the actual metal are different. The other day, I had the truck pretty heated and had to shut down and run inside (I was running errands--don't remember exactly where). I let her get down to about 325-350, and shut her down. When I came back, the temps actually climbed to over 400. The heat was dissipating from the metal, but the heat inside couldn't go anywhere. It was being held in. This was due to how saturated the metal was with heat. When I shut it down, the flow over the probe looked like 300-350, but it couldn't measure what the metal temp was. And when there was no more flow, the dissipating heat showed what was really happening.
I have found that the best way to get temps to go down quick, especially if you know you are coming to a stop somewhere and will want to shut down, is use a lower gear. When I'm on the interstate towing, and am getting off to fuel, I shift down (5th, or maybe 4th) and let the engine slow me down. Just taking it out of overdrive if you have an auto will do the job. Usually the length of the off-ramp is enough. This increases the flow of air thru the exhaust without actually burning very much fuel. Therefore, it is much cooler air. This gives the metal a chance to dissipate the heat, and the flow takes it out. Then I milk it to the pump. If temps are still a little high, I just raise the rpms to about 1200 for about 10-20 seconds. Let off the throttle, and temps will drop below 300. This has always worked well, and isn't really that inconvenient.
SOLER
I have found that the best way to get temps to go down quick, especially if you know you are coming to a stop somewhere and will want to shut down, is use a lower gear. When I'm on the interstate towing, and am getting off to fuel, I shift down (5th, or maybe 4th) and let the engine slow me down. Just taking it out of overdrive if you have an auto will do the job. Usually the length of the off-ramp is enough. This increases the flow of air thru the exhaust without actually burning very much fuel. Therefore, it is much cooler air. This gives the metal a chance to dissipate the heat, and the flow takes it out. Then I milk it to the pump. If temps are still a little high, I just raise the rpms to about 1200 for about 10-20 seconds. Let off the throttle, and temps will drop below 300. This has always worked well, and isn't really that inconvenient.
SOLER
