Hard to start facing downhill

I wonder if the gas is seeping into the EVAP system since the tank is full and parked on a angle. Is the check engine light on? Never the less this is a possibility, you should have the vehicle scanned for any trouble codes, even if the check engine light is not on. You just never know.

No Check engine. Used to happen (in same location) when wet. I kick it out of garage for wood projects - sits overnight in nasty rains. Thought I had ignition issues but replaced all that 5000 mi ago. Perfectly dry day - four hours, had to crank for 10 - 15 sec before it fired up. Only bucked a couple times while cranking.

Besides the EVAP idea, then you should check the fuel pressure. It should be 56 to 63 lbs. and do a fuel bleed down test at the same time. Just a matter of letting sit for 5 minutes, to see if the fuel pressure drops. It shouldn't drop more than 5 lbs.

Thanks RF - If fuel pressure is low, or bleeds off by 5lbs in 5 mins, is that indicative of fuel pressure regulator or the fuel pump? (Likely my mileage may vary)

When testing, with the key on the fuel pressure should be normal or close to it. With the key off and the fuel pressure bleeds off, then it is the spider fuel injection assembly. This would have to be replaced. You never have good luck trying to repair the spider assembly, you always end up with the same problem. This is what that looks like.... https://www.carid.com/2001-chevy-silverado-fuel-delivery-parts/delphi-fuel-injectors-24569693.html

So, if there's bleed off with power off, what causes it not to start on a slight incline? Fuel leakage out of the spider? I'm just trying to wrap my head around the "starts good on the level" versus Turns over and barely fires on an incline thing. I appreciate the tutorial.

I don't know for sure, I'm just giving you most probable causes to check, that you can do.

Really the only thing that makes sense is if there is a problem with the EVAP system. When that gets saturated with gas it is hard to start.

Copy that!