I would like to mention something, since the original question was about using the big rig truck pumps vs RV lanes at Flying J or Pilot. Some have mentioned the downside of not being able to pay directly from the truck lanes. Pilot/Flying J does offer the RV Plus card, which can be used to pay at the pump at either RV, Auto, and Truck Diesel lanes.
You can apply online and they do a credit check on you, since basically they are administering you in a similar fashion to their commercial fleet customers. You call up your outstanding balance online and pay with a draft on the bank account of your choice. You have an online ID/password with them and a PIN for use at the pump with your RV Plus card. They do not bill you, you must go in and check on line routinely and pay the outstanding balance by the due date.
I have inquired as to the availability of this type of arrangement for non-commercial customers from other major truck stop chains such as Loves. It is not available at any others that I have found.
I now preferentially stop for fillups at Pilot/Flying J when I can, even though I think Loves are impressive, well run truck stops. Pilot/Flying J has extended this courtesy to me as an RV customer, telling me they value my business. Loves does not extend this courtesy, telling me they value my RV business less than Pilot/Flying J does.