I have a 95 z71 and m not much of a mechanic, but try to learn as I go. When I take off my truck sounds like it has an extra fan or perhaps is turning an extra gear or something. Then after it gets warmed up it will "relax" and it sounds as if something has turned off. I don't know whether it's something to do with the trans. oil cooler, or perhaps there is an extra fan on or something, but it feels like the truck is really laboring and then (especially once I get to third gear and baby the throttle) the sound will go away and the laboring disappears. I'm wondering what that is and if there are adjustments I might need to make.

I've also noticed it does it when it's really hot too. Any ideas?

My 95 2500 2wd does the same thing,its the fan clutch. I looked at it like this,when you can't hear that anymore its time to replace. Also was told it was the hd type.

The fan clutch has thermostat mounted on the front of them. When you first start the motor the thermostat is set to let the fan clutch turn freely and then as the motor/radiator heats up the T/stat connection on the front engages the fan to get more air moving across the core. The noise that you hear is normal, and the fact that the fan quiets down as it warms up is good. If you want to test this, go out and turn your fan before you start the truck and feel the resistance of the fan blades to the motor. Then start the vehicle and warm it up, then shut off the motor and try turning the fan blades again--see if you feel a difference in resistance.