The hard start after 5 minutes, combined with poor MPG, AFTER doing injectors, makes me think you have an injector that isn't closing all the way.
When this happens, fuel continues to leak from the rail into the cylinder after engine shut off. The extra fuel in the cylinder keeps makes the condition too rich to start (or just a rough start)
Eventually, though, the pressure in the rail is drained and the fuel leaks down past the cylinder rings - so the engine will start again.
Of course, gasoline is a solvent and will ruin the engine oil. So, there is that.
I suspect you have a leaky injector, dude. Get a fuel pressure guage and check pressure at the fuel rail. with the engine cold, engine warm and recently shut off, etc. You don't want to see the fuel pressure at the rail dropping very quickly after you shut down the engine. There is a check valve in the fuel line, for one thing, and hte injectors should be sealed for another.