Not really a mod but my latest acquisition for the trep is a bluetooth OBDII scanner - ELM327 from Amazon. Works perfectly with my laptop or with my phone. Log data as you drive, clear the CEL etc etc. The limit is the software you choose to use with it. Of course being OBDII it's not 'trep only' but will work with just about any vehicle that adheres to the OBDII protocol, it's also small enough and low current enough to leave in place as long as you want to.