Hi this is Dusty, I'm one of the auto experts on RepairPal's Car Genius team!
Sounds like you've been dealing with quite a headache.
The downside is that those codes don't point directly to a component failure, what they do point to is a symptom.
The P0455 is for a large leak within the evaporative emissions system, this could be due to a failed electrical component, like the purge valve, or a vent valve.
Which could be stuck open resulting a leak condition and may or may not be accompanied by its own unique fault.
It could also be caused by a compromised hose, gasket/seal, or test port (if equipped).
The P0496 indicates a high purge flow, which is most likely a secondary result of the leak in the evaporative emissions system.
I understand the hesitation of the financial burden, but it sounds like you've already invested some funds into replacing components that ultimately didn't resolve the issue and may have covered some or all of the cost of a comprehensive diagnosis.
This is why a thorough and accurate evaluation by a qualified professional is critical, there are special procedures and equipment specifically for evaporative emissions diagnosis to aid in pinpointing the issue.
As for the noise from the fuel pump that could just be symptomatic of the replacement part, or an indication that there's a potential problem with it.
If you have any other questions or would like to help with finding a RepairPal Certified Shop to evaluate your Lucerne in your area, give us a call!
877-913-1554
