12 Ply Trailer tires and MPG drop

So I just put on new tires all the way around my truck. I kept the truck tires at 10 ply but jumped from 10 to 12 on the trailer. From this point on, my MPG has suffered. When empty I was getting about 14-15ish MPG around 70 mph. Now I'm getting around 12ish MPG. Loaded, it drops a lot more. Im carrying a payload right now of around 7k lbs and I would typically get like 11 MPG but now I'm getting around 9 at 70. I dont even want to find out what a 15k load is going to do to me lol.

But I'm assuming it's from more rubber grabbing the road? Anyone able to explain the dynamics of the different ply and how they affect MPG? I increased the tire pressure to see if it would help. I was at 80 but temps dropped to low 70s cold. So while driving up here in Wisconsin I upped the pressure to 97 while hot. Didnt seem to do anything.

Thanks for the discussion.

 

Yeah, that's what I was thinking. So as they wear down, do you think the mpg would get better? Lol, about to do a bunch of uturns!! Just joking, those tires werent cheap and I need them to last.

 

They are radial. The truck tires are 10 ply Mastercraft courser hxt. The trailer's are 12 ply power Kings Towmax STR. I have 90 PSI in them currently but max is 100.

Mileage really hasn't gotten better. Changed the fuel filter, that was kinda dirty but it was time for a change anyway.