I would check the ground on the back of the right side cylinder head right beside the oil filler neck on the side of the head that faces the firewall. It's a main ECM ground and if this is off it will cause a misfire. That's for the first set of codes you said (P0304)
For the next code the P0355 i would take your crankshaft position sensor out and look at the end of it, It's probably hitting on the reluctor wheel. If it has any scuffs or white marks on the crankshaft position sensor it needs to be shimmed with a 0.5mm thick shim. GM part number 12565102.
While your looking at the sensor take a quick look at the front cover and make sure it's not damaged.

 

The sensor looks fine replaced it anyway no luck yet checked all grounds nothing im leaning towards distributor MY TECH IS SCREAMING COMP.

 

I am haveing the EXACT same issues with my 01 blazer (102k miles)....I had the water pump and intake manifold gasket replaced and about a week later tach goes nuts getting codes P0300 and P0335. Replaced CKP sensor and it didn't help at all. No damage or marks in old sensor. Any help would be greatly appreciated.

 

Have you checked the wiring for any signs of damage? Run a continuity test on the wires between the CKP sensor and the PCM?

 

Well good luck because it went to five shops two of them were chevy dealers one i really trusted ,one shop was a custom hot rod shop all they want to do is change parts, ends up costing thousands of dollars, zero results,the last thing i did i took it to an electrical guy who had it for three days he started calling me trying to raise the estimate for repair higher so i stop the bleeding right there ,he offered to buy it for peanuts and i sold it to the electrical guy well he calls back claiming the motor was shot so not to sure but maybe they dropped something in the motor and after all the crap i went thru i still not sure what happened por what was wrong ,oh ps i put new ac delco computor new complete brand new ac delco distributor new sensors ,new complete spider injection etc etc etc no luck the sad part is it kkk booked at 5800 and sold it for 2300 not to mention the cost of trying to repair $$$$$$$$$$$$ so im just saying be careful

 

No I have not run a continuity test...I think I am going to try a repair shop. I am not willing to dump tons of money into to this buit I would like a pro to look at it. Hopefully I will have more luck than Mike12657. We will see what happens.

 

Just to let you know the repair was a new crankshaft position sensor, and throttle position sensor. Total for parts and labor $205.

 

I know what it is . I have same problem on my 2002 4.3
gear on bottom of distrib. Worn out,
this is third one i had put in $500 min.
Be lucky to get mine back running this time.
Bad design by chevy. Nice suv, hate the motor

 

i have a misfire on my 02 blazer 2dr and the computer said misfire on cylinder 3 i replaced plugs and wire and doin cap and rotor and coil soon any tips

thanks

 

we have the same problem but on mine the crank sensors hiting the crankchaft