How's it going everyone!

I've been driving for a few weeks with code P0455 coming on occasionally. I finally got a new gas cap and that seemed to fix the problem for a day. Then I got a service engine light and same code. Took it to my shop and he said something about a code T1000 ( that may not be 100% accurate, I didn't hear him exactly). The dealer says the part costs $800 and change, my mechanic wants to charge $1300 and change, and Atlantic British has the part for $140 (obviously not genuine).

My question is this, given the premise is correct, what's the easiest way to fix the problem? Am I able to replace the pump easily and at what cost?

Thank you