Make sure you only get the proper gas cap for that vehicle. DO NOT use a generic gas cap.
My 97 Dakota started throwing codes after I installed a locking gas cap. Changed back to the OEM and the code went away.
Also check all the hoses for the evap system. Maybe something worked loose.
Check all your vacuum lines as well. Maybe there is a crack or a broken joint or something that is not all the way gone but enough to reduce the vacuum enough to throw a code.
Inspect everything first. Look, touch tug a little before you start replacing stuff AND check that new gas cap.
