Is your coolant temperature sensor new? or original? that can affect cold engine operation and fuel economy, maybe even possible starting issues.

 

It's original as far as I know, however I have no issues with temperature indication or cold-running performance - only starting.

I really am thinking fuel now, as if it won't ignite readily and just floods the engine. Foot hard to the floor allows for a shuddery start - running fine from then on.

 

Your fuel pump is on borrowed time.
Intermittant engine function when fuel pump is failing.

If ECT is original, replace.

Use factory parts.

 

I'm still a big believer that you got a tank of bad gas, I guess this will be my theory until I'm proven wrong. I always search for the "easy" things first, too many times people start looking for more than what it actually is. A good rule thumb for fixing any problem is to keep it "simple" first, and then progress from there. Good luck.

 

And cheapest. If ya keep it simple it's usually cheap.
But on the flip side of that, years ago when I first had the acceleration problem I didn't listen to people and do the simple fix of the ECU, or the cheapest. I didn't want to believe that a simple tiny capacitor could ruin the whole car. But when I finally jumped on the bandwagon and switched the ECU everything was fine, til that one also went.
My 'ol man used to say keep it simple stupid.

 

I couldn't agree more. If there's one thing I learned the most about our LS cars is that they are extremely well made, a ton of time, ingenuity, and money went into building these awesome machines, so yes, I always look for the "simple" stuff first, because that's generally what it comes down to with these "beasts". At least in my humble opinion. Best of luck everyone.