PO340 2003 Trailblazer ... and others

One day I drove my TB to work with no issues, about a 10 mile drive. When I left for the day it was hard to start and when it did start it was missing. I tried to drive it home but the SES light started flashing. I pulled over, shut it off, let it sit for a minute then started it back up. It then ran fine. I checked the SES and got a PO305, cylinder 5 misfire. I then changed the spark plugs which were pretty old.

Then the next day it ran fine going to work. Again it started missing on the way home. I pulled over again shut it down, restarted it, but this time it didn't fix it. When I got home I got a PO300, multiple misfires. I then ordered a new Camshaft sensor, which was pretty cheap, then tried again.

The first day it ran fine. Then one day I drove to work, no problems, but on the way home it started missing again. SES said it was a PO340 this time, Camshaft circuit. I checked the ground and the power lead which were fine. I also checked the fuel pressure and the vacuum which were also fine. I then poured Sea Foam into the gas tank thinking the injectors were clogged, which seemed to clear it up, but it didn't.

Now, some days it will run fine. Other days it will run fine going to work but miss all the way home. It seems after it has sat overnight it is fine.

Is this purely an electrical issue or could something in the gas be causing this?

The TB has 180,000 miles on it. It's my work beater.

Thanks.