Everything so far leads me to believe that its the fuel pump. I really cant think of anything else that would be wrong. By the way if you are spending $350 on a fuel pump you are spending way too much. Got the one for the 98 for $260 at autozone in arizona.I dont know what autoparts places are around where you are but i would price shop a bit.

 

Ok I replaced the pump af ew weeks ago and it starts up and runs fine. Prior to replacing the pump I replaced the fuel cap because the scan lead to that not keeping pressure . With the new pump in it still has the CEL for the same thing. Any specific spots in the fuel system that are prone to this type of seal leak that would cause the tank and system to not hold pressure?

 

There is a pressure sensor on the fuel pump housing for the Evap system...it could be bad....or when you replaced the pump the seal is not correctly fitted to the tank..... or there is a small crack in the fuel pump's plastic holder....the line going into the tank for the Evap system might be cracked or worn...check all the connecstions/hoses for the Evap system...

 

I also have an '02 Blazer experiencing the same thing when it is dmap or raining and haven't started it for a few days. When it first started, replaced the distributor cap with a new one. Seemed to work...for a while. Through our drought I forgot about it as there wasn't an issue...then last weekend after coming home from work Friday and not starting it til Monday (and raining for four days straight) it wouldn't start. Gas was good and all, just cranks over with starting. My suspect is maybe a bad or cracked coil, but have yet to test it. My daughter's Honda did the same thing and found a crack in her coil and fixed it. Donno, may be worth investigating and will let you know.