I just bought a 2002 Blazer with a 4.3. It had a DTC P0301 #1 Cylinder misfire. I replaced the spark plugs, wires, distributor cap and rotor. The code came back after about 15 miles. It has a rough idle. It will occasionally 'stumble' under load. I checked the throttle position sensor with my scan software. It measures the % applied. It seemed to measure okay from 0-100%. I'm thinking injector, crank or cam sensor?

 

Checked the compression on #1 cylinder, 90 psi. Squirted oil in the cylinder, it didn't change. The other cylinders are around 140 psi dry. Sounds like a burnt valve or blown gasket.

 

i would go with the burnt valve part