hesitating/ no start

my 97 blazer with a 4.3 vortec was hesitating really badly when accelerating so i put in plugs, wires, cap, rotor, and ignition coil and also a new egr valve. when it rains or there is moisture in the air it starts to hesitate again sometimes and today it just wouldn't start. any ideas????????

You need to check for proper and full fuel pressure and for lose of spark.
Check for good spark to more than one spark plug.
Post back fuel pressure and if good spark.
Has it had a check engine light on or flashing?
MT