You can get a snowball reaction when you actually fix a small leak, but cause a bigger problem when you introduce air into the system.
I've had some experience with air locks on my 5.3
I discovered any time you open the cooling system on this engine it is very hard to bleed the air out. The air will stay trapped in the block an cause the engine to overheat, even days later.
First be sure you do not actually have an external leak, you don't need to waste time chasing something that is not the cause of your problem.
The small bolt to just behind the alternator, above the thermostat can be loosened to bleed the air out. If you have a cooling system tester it is very easy and you don't even need to run the engine to bleed the cooling system.
Top up the rad, run the engine a bit if you don't have the tester. Once the rad is full, put the the tester on and loosen the bolt slowly. If you don't have a tester, put the cap on and start the engine.
If you are using a tester you will need to pinch the overflow hose to keep the pressure in the system.
With the tester pumped up it will bubble air out at the loosened bolt. If you are running the engine, as it warms up the pressure will purge the air at the loosened bolt.
When only coolant flows out, tighten the bolt and shut the engine off, or remove the tester.
Now run the engine and make sure that both rad hose get warm as it nears operating temp, indicating coolant is flowing through the rad. Both heater hoses should start getting warm shortly after the engine is started, indicating the pump is moving coolant through the system.