98 Blazer leaning out at full throttle

[RT Big Block]

I am so ready to go nuts ! I have 98 blazer that leans out at full throttle but if you lift a little it start pulling again. When you give hard throttle the O2 sensors voltage drops to 0.492 showing it leaning out . I have no vacuum leaks I Just replace intake gaskets my fuel pressure is 60 lbs. and does not leak down . Here the weird thing after I stop and put gas in it when I start it up it try to died when I pull back on the road. So does anyone have any idea what wrong ??? Thank !