Any help you can provide is appreciated. Vehicles are so expensive now trying to keep this one going but we have these dam emission test coming in JAN. if you fail with any codes you cant buy a plater sticker. such a scam.
2007 jeep grand cherokee. 4x4 5.7l hemi. 155,000 miles.

PO524 oil pressure too low - I have replaced the pressure sensor several times but this always comes back. do these sensors break that quick or can it be something else?

PO457 loose fuel cap - mechanic put a gasket around the fill tube and replaced the cap but code still persists
PO456 small evap leak- what can cause this?
PO440 general evap failure - what can cause this?

lastly the gas tank skid plate has rusted away and they seem in short supply. any ideas? does it actually hold the tank in place or just for protection?