Based upon my experiences with my 2009 Yukon 5.3, (I am not a mechanic) the smell of gas and longer starting times is likely an evap issue. There is a air line near the filler neck that is supposed to draw in those vapors into an evap canister, hold them in the canister until they can be reintroduced into the fuel rail to be burned. There is an evap solenoid that controls the vapor movement on the canister, and a purge value on the drivers side of the engine (on top) that creates the suction. As the system attempts to pull those vapors into the fuel rail, your engine is not getting the vapors and is hard to start. One of those components or very possible, one of the lines is probably failing. Many threads on this issue in the forum. I am surprised that you don't have a P0442 code. You might still have the codes pulled jus to check because sometimes the check engine light no longer works (mine does not).
He most likely doesn't have a code because it isn't an evap leak. An evap leak is a leak on the air volume of the fuel system, not the liquid volume of it.
If the leak is happening after the fuel has been sent out of the pump in the tank, that is no longer metered by the evap system. The only malfunction indicator that would help in that case, is a fuel pressure sensor that shows the vehicle isn't building enough pressure with initial key on, but his vehicle doesn't monitor fuel pressure.
And evap has nothing to do with starting the vehicle, there is no draw of fumes that goes into the fuel rail to help it start, the evaps only job is to relieve the pressure in the fuel tank. In the old days the tanks were vented to straight air, but they gave off fumes and stunk. All the evap does is open a solenoid when the tank gets pressure, and the engine sucks in the fumes. Heck, the evap might not even be open when the vehicle starts if there is no excess pressure, it certainly can't be relied upon to help start the vehicle.
