Why is my Tahoe smells like gas

I agree with Klaus, likely a fuel line leak. I live in Northern Ontario Canada, a lot of salt is used on highways here in the winter, which causes big rust issues, especially with brake lines and fuel lines. Get under the car and take a look at the fuel lines that run from the tank to the front of the vehicle, look for wet spots. There are two lines, one is a high pressure line running from the fuel pump on the tank up to the engine, the other is a return line. There is likely a third line running over to an evaporator canister, sometimes near a fenderwell, or sometimes even at the front of the vehicle. If you are not smelling fuel when the vehicle is off and has been parked for a bit, it is likely the high pressure line that is leaking when the fuel is under pressure. If you do see a wet spot, you can likely confirm by having someone turn the key in the ignition to the "run" position (without turning on the vehicle), this will turn the pump on in the tank and pressurize the line, and you might then see more fuel coming from that wet spot, or maybe a drip. If you are in an area where road salt is used and need to replace fuel lines, I suggest that you replace the steel lines with Nylon fuel line meant for fuel injection systems - won't rust and is a lot easier to run.