1996 Chevy Suburban 1500 5.7 Starting problems

I have a 1996 Chevy Suburban 1500 5.7 with 175K miles. 1 year ago for no reason it would not start for 20 minutes then instantly it started. No clue what happened. 4 months later if I let it sit for 3 or 4 day's I had the same problem. It turns over fine, then 5 to 10 minutes later it finally for no apparent reason would start hesitatingly. When this happens it runs and starts fine for day's. It only had this problem after sitting long periods. It seems it would start just as you are letting off the key and it sounds rough like partially flooded. I had better success when I only turn over for 2 seconds at a time. Then it got worse to just sitting over night. Then sitting for a couple of hours. Now I can't start it at all. I have changed the starter, fuel filter and had the test done on the battery and charging system all is OK. I hear the fuel pump when I turn the key. I sprayed some starting fluid in the carburator but not a flinch. I thought if it tried to kick over it would seem like a weak fuel pump. Does this eliminate the possible fuel pump problem? Does that make it an electrical problem now? HELP PLEASE!