Codes P0446 And P0300 On Silverado

[smus9917]

I have a 2000 Silverado with 235,000 miles on it. I have never had the valve cover off this truck and its been great. The service engine light has been on for about the last 100,000 miles and I had it read. It came up as a faulty vent sensor and I was told not to worry about it. Recently, the truck has began to stumble a little bit when I get on it and shake at red lights and drive thru's. I had the codes checked today and they came back as P0446 and P0300. I was wondering if anyone has had these codes and what they did to fix them. The P0446 seems to be related to the EVAP vent solenoid and P0300 reads as a random cylinder misfire. I should mention that the fuel pump was replaced with a gm factory pump and has about 70,000 miles on it, about a year ago I made 8mm racing plug wires and put them on, and about 3 months ago I replaced the plugs with acdelco platinums. Also, I have checked for vaccum leaks with WD-40 and listening for engine revs. Please let me know what you think the problem could be. Thanks.

[ChevyTech007]

You need to have it scanned at the dealer to see which cylinder or cylinders are missing for the P0300. Your evap code will not cause the evap code. You have two problems. A vent solenoid is probably the cause of your evap code.