I've not installed an aftermarket stereo in the Tahoe, but I've installed dozens of others in many types of vehicles. I know I've seen similar wiring harness adapters in the car audio stores, leading me to being relatively comfortable with what I'm saying here.
You'll need to get one of those wiring harness adapters. A bit of an added expense, but well worth the investment. You'll still need to make your connections to the new stereo, but all the leads (power, ground, speakers, dimmer, etc.) are in the correct location relative to the factory harness.
It is also possible, given that the factory head unit is not the same size as the aftermarket units, you'll need an install kit so that the new stereo is properly located in the factory mounting area. It should also clean up the space with a blank or another storage area.
I'm not sure on the factory amplifiers and if they play into the equation, but some factory set ups require you to by-pass the factory installed amp in order to get the correct sound from the factory speakers. This usually winds up resulting in less quality sound than what you had from factory, so replacing the speakers and adding an aftermarket amp is possible as well.
Prolly the easiest thing to do, if this post doesn't help you at all would be to consult any reputable car stereo shop. Those guys are usually pretty helpful.
Good luck!
D
