Tranny Temp Gauge Not Working Right

[04hd]

So i have not had a single problem with my tranny temp guage. I have towed my car to new jersey in 70 degree weather with it never getting to 200. I put a plow on the truck and now it gets hot after like 10 mins of driving. The normal engine temp is fine. When i checked the fluid after looking at the gauge and it saying 180 it was still ice cold. Do you guys think the gauge is off? I know the plow might be blocking air but i tried turning it and dropping it like 2 inches off the ground and no difference. The temp also rises when idleing at a light. Any help would be great.