What is making my 1996 GMC Sierra K1500 misfire?

[JustMaybe]

My truck is misfiring while driving on the freeway. It was doing it really bad and had to take it in. Got the injector spider replaced and it drove a lot better. Before I took it in I replaced:

1. Both O2 sensors (pre-cat)
2. Camshaft Position sensor
3. Crankshaft Position sensor
4. Spark Plugs
5. Plug Wires
6. Cap and Rotor
7. Fuel Filter
8. Cleaned MAF sensor
9. Ignition Coil

The truck is running great except when on the freeway it still has a slight misfire. The fuel mileage is down, but power seems to be normal. The check engine light only comes on if I drive it long enough. The code is P0300 which stands for "Random Misfire". I have replaced the EGR valve (electronic) within the last two years. I was thinking the distributer gear might be the problem. Also, about 50% of the time at start up it misfires and the rest of the time it fires perfect. I can always feel the motor shaking a little because of this slight misfire, but it doesn't seem to effect the truck while driving around town.

 

[boogie_4wheel]

I would pull the distributor and check the gear (driven by camshaft), which you also suspect.

I have heard multiple times of the gear being worn down and causing a random misfire, or a misfire on the same cylinder(s) every time; such as a P0306 indicating that it was the #6 cyl). If the gear is worn, or if your distributor shaft has any side play, replace it with an aluminum housed unit, versus the stock plastic one. No more worrying about any stripped threads that hold the dist cap on. Speaking of that, neither of your distributor cap mounting holes are stripped are they?

Do you have any large amounts of build up on any of the plugs? This would help locate which cylinder(s) are causing the issue.