95 Blazer: Water in the gas Tank?

I have a 95 blazer 4wd. I am at my wits end with this thing. 2 months ago it started to idle rough. After putting in STP the rough idle stopped until I filled up with gas and the rough idle began all over again. My father has replaced the spark plugs, fuel pump, checked the hoses for leaks and pulled and cleaned the egr valve. This problem seems to go away when I put a fuel dryer in the tank. It would run fine after a few fill ups but starts out of the blue after i've been driving a few miles. Do I need to take my fuel tank off and dump it? Tonight it started the rough idle again and was putting off an odor. I have put chem b12 and a dryer in it. Any ides?

Yea, do a search for cpi injector

If you're going to the same gas station, the problem could be with them. Try a different high volume station for a while and see if there's a change.