Do you always have to pay inside at Truck stops?

Get a fuel card! I got a TSD Logistics EFS card last year. It works at most all the truck stop pumps and gets a discount if available.

You have to link to a bank account and payment is automatically deducted from your account within a day or two. Just set up a extra bank account to use for it and only keep fuel $ in it.
The name changed recently to Open Roads.

Link - https://myopenroads.com/

You only need to go inside if you want a receipt or snacks. (my wife is much happier!)