1997 blazer 4.3 with rough idle and stumble off idle
 

Hello,
I need feedback, this is what has happened i first had a cyl 5 missfire and it was a bad missfire ( you could really feel it code p0305 i believe) and all of a sudden it went away ran great , i cleared the codes.Then i get a real bad missfire again this time it said cylinder 3 missfire i changed the plugs and they were clean and not fouled !!!So after hearing about these spiders on these motors i decided to replace it , well i dont have the bad missfire anymore and runs relatively good except for the idle it kinda oscillates and feels like it is losing a plug once in a while !! It used to run great before all this started happening . Here is the new parts i have thrown at it - ac/delco fuel pump yesterday pressure was 52# before now it has 56 -60 key on engine off !! new spider (standard motor unit updated model) new ac/delco plugs,wires,cap,rotor,fuel filter !! Today i got a p0303 code again after it idled for like 15 minutes!! here is some data i collected before the light came on (sorry i dont have the freeze frame data at code set)
mil status- off & idle was 586-615 & maf lb/m is 9.7to 10.00 coolant was 189 & iat is 75 & ign adv is 16.5 to 24& st ftrm1 is 0 to 2.3 & lt ftrm 1 is steady at .8 & o2 reading is fluctuating from .050 to 890 !! The thing i see that looks LOW is the map hg reading(if that is the vacuum reading)??? PLEASE CHIME IN !!!!! IM AT MY LAST NERVE WITH THIS TRUCK....

Update i put the vehicle on the tech2 and saw missfires on cyl 3 mostly and then cyl 4 and then misc other cylinders , i think i have a distributor issue so thats gonna be ordered,,,,let you know what happens