What I'm trying to say is that non commercial non CDL 78000+ farm trucks are subject to the same inspections in a DOT stop, so it's not the commercial/for hire part that triggers the law, that's all.It's possible, but I don't think you have to worry.
Look at it from the Leo's point of view....why hassle you over 20 gallons when he could nail a semi with maybe 250.
Kinda the same with speeding tickets. What could hang you up for maybe $75 can cost a trucker $800.
If you are commercial/CDL they can look at whatever they want, whenever they want.
I think they've laid off the pickup trucks to some degree but they were sure after them 15-20 years ago when diesel pickups really hit the market.