[Number 3]

First question, did your lease say you could make modifications to the car?

Second question, did you tell the Chevy dealer that you had modified the car?

In your original post you said it had mods, but you didn't say you made it clear to the Chevy dealer that you had. If this in fact violated the contract and you passed it off on the Chevy dealer that may be what's going on.

That being said, unless you misrepresented the car or they didn't check until after the deal was concluded, I'm not sure what recourse the dealer has............other than you bringing the car back out of your own kindness.