Charged 3- or 4- axle price on Grand Parkway between 90 and Westpark?

My wife noticed that she was being charged various prices going up and down between Westpark and Highway 90 on the Grand Parkway (4 booths). I checked my account, and found that my motorcycle always got charged the 42 cents quoted on the sign, but that my car had been charged 84 cents or $1.26 at the same booths, obviously multiples of 42, and the stated prices for 3 or 4 axle vehicles (I have a Mazda6, not pulling anything). These booths are administered by Fort Bend County. I called EZ tag, who told me to call Txtag, who told me to call Fort Bend, who told me to call EZ tag. When I called, a couple of people suggested the other organizations might have variable rates, but I’ve seen nothing on any of the sites to support that. But if my wife and I are both seeing this on our separate accounts, there must be others. The booths north of I-10 are administered by HCTRA, I think, and I haven’t noticed anything funny there, and I’m not sure about Beltway 8, or other sections of the Grand Parkway. But wondering if anyone else is seeing this? Not sure when I can check this thread again today, but I’ll respond as quickly as I can if anyone has questions.