Subsequent to setting up my new Trezor I sent a small test amount of BTC from my Ledger wallet to the BTC walet address in my Trezor wallet (successfully). I then sent a larger amount. Subsequently, I did not see the total amount in my wallet that I should have (less gas fees). I looked at the details for my transaction and found a second OUTPUT address in the smaller amount that seems to have diverted a few hundred dollars of btc. Is this normal and the second output address still somehow connec ted to my trezor wallet and accessible or have I somehow been robbed?
From your description, it looks like the second transaction you mentioned is a transaction to your change address.
I can see that you already opened a ticket with our support. Please, find a detailed explanation in the ticket.
General explanation of change address can be found for example in this thread: Does Trezor have secret addresses?