Chevrolet Repair: 6L vortec bogging down, coolant temperature sensor, throttle position sensor

Question
I have a 99 gmc 6Litre vortec, 4 x 4.  Have an intermittent bogging situation usually whan cool.  Took it to the shop, fuel filter changed along with a new fuel pump installed.  Plugs were changed as well.  I have a camper on the truck and when this happens I can put my foot to the floor, engine is running fine but there is NO power and usually it has lots.  Any help with this appreciated.  No codes have been tripped for any of this.  I hate wasting money on repairs not really needed.

Answer
Testing the fuel pressure, especially during the problem, is what I would do.

If the pressure is up to spec, I would test the throttle position sensor.

Coolant temperature sensor accuracy is also important. Here is a very interesting link about that.

http://www.chevytalk.org/threads/showthreaded.php?Cat=0&Number=1366279

Van