95 starts when floored only

[Psode27]

I'll try and keep this as short as possible.. Basically, truck was running better than it ever has (after new tps, IAC, coolant sensor), parked it in my garage (Thank God..) and it wouldn't start. I had just changed, as in minutes before the last trip, TPS, IAC, and coolant sensor. I was diagnosing a high idle on startup and it was wandering gears at around 60mph. All issues were corrected the last trip and things were looking great!
The next time I went to drive the truck, it fired right up, idled several seconds around 400rpm, and died. It would not start after that. I checked ignition module, and it checked okay (4-5 times), put new coil in it, cap/rotor/wires within 1000 miles or so, fuel pump relay (54 code), recent fuel pump, oil pressure sender thing (under distributor, forget what its called), probably more I'm forgetting.
Today, after changing the relay, we just randomly floored it while trying to start it. It started! It didn't idle, and we had to keep it alive, however it eventually ran great. Took it for a drive and it was very uneventful, no loss of power etc. I shut the power off and it wouldnt re-start without flooring it again (when warm), however idled great (warm). Hanes manual, and youtube talk about setting base idle after an IAC valve replacement. It idles great warm, I hate to completely jack something up troubleshooting.
I am suspect my timing may be off from moving the distributor around (though I made good marks), could that affect starting that significantly?

Any help appreciated! Truck has 200k mi, all stock, 5.7...

 

[Chewy1576]

What year is your truck? The IAC behaves a little differently with the pre '93 and '94-'95 ECMs. Checking your base timing probably wouldn't hurt in any case. If your truck is '93 or earlier, there is an IAC relearn procedure so it's position matches where the ECM thinks it is (http://www.gmtuners.com/tech/TPS_IAC.htm). The '94-95 ECM's do their own position calibration every time you turn off the engine so it's not really necessary with them, but you could still have to adjust the idle screw. You could also have leaking injectors that are flooding out the intake, which it why it will only start with the pedal to the floor. There is a flood clear function in the ECM that if you hold the pedal down when cranking, it won't fire the injectors.