I have a 2001 chevy blazer that is missing i have already replaced the distributor ,cap and rotor button and the plugs and wires what else do i need to check

if its the gasket then need to replace it --other then that have you tested the valve train --compression test --cam shaft

What year? Does it have a distributor? If so, possible distributor cap/rotor issue. If coil over plug, you need to run a compression test to see if a cylinder is weak/valve issue

P0305 is a misfire on number 5 cylinder replace spark plugs, wires cap and rotor button. Please note: Does the ac cooling line/hose go over top the distributor ? If so GM/CHEY had a problem when dripping from that AC line/hose dripped down onto the distributor. That caused miss fires after a time. I hope this helps, Lee.

Could be the EGR valve or the idle adjust valve. Check Engine light on? Any codes?

Check the plug wire from the ignition coil to the distributor cap.
If you haven't already, replace the distributor cap and rotor.
The GM Vortec's have issues with moisture getting inside the cap and rotor and causing problems.

I’m happy to help further over the phone at https://www.6ya.com/expert/jason_00b31cc8f593773a

If you already replaced the wires, I would suggest replacing the plugs, distributor cap and rotor. They are also very important parts of the spark. Fuel injector problems can also cause misfires.

Remove cylinder # 1 spark plug, # 1 is the front one on drives side, turn crankshaft pulley to TDC on compression stroke, you'll feel the comperssion at cylinder #1 spark plug hole, follow cylinder # 1 spark plug wire to distributor cap, mark outer part of distributor where # 1 sits, remove distributor and restabe distributor with rotor at mark you made, then set timing.

Disconnect the wires and take pictures with cell phone for reference to ensure you don't cross them when reinstalling the new distributor cap. Remove the two torque screws in the distributor cap and remove the distributor cap to access the rotor. Remove the rotor by lifting straight up and inspect the distributor for any condensation and corrosion. Clean the breather screen at the bottom of the distributor before installing the new rotor which just slides back in place. Install the new distributor cap and tighten the new torque screws, make sure you do not over torque the screws since the distributor housing is plastic and prone to stripping. Reattach the spark plug wires and start the engine and idle for 5 min and go for a test drive. Good luck and you may want to also buy spark plug boot lubricant to ensure the spark plug wires are fully installed when placed back on the new distributor cap and recheck connections after test drive. Keep me posted, be glad to know your blazer is running 100% and please rate.

The firing order for a Chevy s10 depends on which engine you have. 1.9L engine the firing order is: 1-3-4-2 . Distributor rotates counterclockwise. 2.0L engine the firing order is: 1-3-4-2 . Distributor rotates clockwise. 2.5L engine the firing order is: 1-3-4-2 . Distributor rotates clockwise. 2.8L engine the firing order is: 1-2-3-4-5-6 . Distributor rotates clockwise. 4.3L engine the firing order is: 1-6-5-4-3-2 . Distributor rotates clockwise.

make sure u have the wires in the correct spots, there is a firing order, u need to have them in the right spots or else it wont fire, call ur local parts store and they will give u the firing order