Ok. Still have the P0455 and now getting a P0442. I reset the codes and the P0442 hasn't come back in the last 24 hours or so. The code scanner says that a charcoal canister can cause both problems and that is the only part that I haven't replaced. I did replace the smaller evap line harness that is on top of the fuel tank since the orings felt a little loose. That was about 2 weeks before the P0442 code started. Just bought some 5/15 fuel hose, a barbet tee, and slid the hose up onto the one tank fitting, the fuel pump assembly, and the fuel filler line. Nice tight fit. Didn't even need clamps. I have replaced both purge valve solenoid and the vent valve solenoid. The vent valve solenoid was replaced with the "Hummer" part. MUCH less expensive. Same valve and connector, just didn't come with the hard plastic line and oring fittings. I just used rubber fuel line and hose clamps. Did all that about a month ago or so. Could the charcoal canister be causing these ongoing issues? Is there some kind of mechanical valve in the canister that could be faulty? It is original and the truck has 187,000 miles on it.