1997 350 3.7 chevy tk while driving with no load on engine it misses ,as soon...

...as you hit the gas it does fine? have put new from fuel filter forward , filter,plugs,wires,coil,distributor,pvc? value , pick at coil.

have done a fuel pressure check , it comes in at 50# with just key on , when cranking come in at 56-58# ???, have to turn key on , off several times before it will start .