Slow to start

Sounds like you are describing a long crank time. If that is correct, you already found the cause of the problem. The fuel system should remain pressurized for days or weeks. When you have a leak, that pressure bleeds down in seconds or minutes. It has to build up again before fuel will spray from the injectors. Normally that pressure will build up sufficiently after just a few seconds, but during cranking, battery voltage is drawn down quite a bit, and that makes the fuel pump run slower. If you crank the engine for a few seconds, stop, then do that again, each time you stop the pressure will bleed down again.

One clue to this is if you turn the ignition switch on, wait for one second after which the fuel pump will turn off, turn the switch off, then back on right away, the pump will run for another second. Do that two or three times, then immediately crank the engine. Each time you turn on the ignition switch, the fuel pump will run for one second. If the leak is not too big, the pressure will come up enough for starting so you won't have to crank the engine for such a long time.

The common leaks to look for are the rubber hoses between the body and the engine, and the o-rings around the injectors.

Neither of the suspects I mentioned will cost more than a few dollars for parts unless GM used a special hose with a crimped fitting and steel line. I used bulk hose for the repair on my Dodge minivan. It has to be rated for fuel injection systems which can run over 50 psi, not for carburetors which run at 3 - 5 psi. The hose costs around $4.00 per foot in bulk at the auto parts stores.

O-rings are best purchased from the dealer's parts department. They will have the right ones for your engine. At the auto parts store, they might try to sell you generic, one-size-fits-all o-rings. They might work fine, but they also might be harder to install if they are harder or thicker than the originals.