P0440 trouble code

So my 2001 Jimmy is throwing a P0440 code with SES light on. The SES light will also flash sometimes especially if driving uphill under load. I assume that means the ECM has detected a misfire even though I didn't feel one. So, this code is supposedly in the evap system. So I changed the gas cap. This did not fix the problem and I still don't hear any hissing when I remove the gas cap after the vehicle sits all night. What should I look for next? Disconnected vent hose? And exactly where is the charcoal canister? Any ideas would be appreciated.

So my 2001 Jimmy is throwing a P0440 code with SES light on. The SES light will also flash sometimes especially if driving uphill under load. I assume that means the ECM has detected a misfire even though I didn't feel one. So, this code is supposedly in the evap system. So I changed the gas cap. This did not fix the problem and I still don't hear any hissing when I remove the gas cap after the vehicle sits all night. What should I look for next? Disconnected vent hose? And exactly where is the charcoal canister? Any ideas would be appreciated.

Look behind the driver's side rear wheel.
That's where it is on my '97.

Two other things to look at while you're under there. The gas filler tube has a vent line/hose on it (the smaller of the two hoses). Check that out. The fuel pump also has a vent line located on top of the fuel tank. You should be able to see these from inside the wheel well.