I mean in many (most?) states travelling in the left lane is a moving violation

Using it to fish for other violations is where it crosses into the fuzzy and sometimes outright illegal

The counter to this is demand that they write you the ticket for the moving violation, don't answer any questions other than providing the legally required license, registration, and insurance, and move on

If they don't have evidence of a crime, they can't detain you forever on the roadside