Yeah that IR gun is really handy, when towing I routinely shoot the tires and hubs and even the brakes. A hot tire compared to the others means something is wrong- usually low air, maybe picked up a nail or whatever. A hot hub may mean a bearing is tight or grease is bad etc. Where it really helped me out though was balancing the brakes left to right on my dump trailer. Had some swing to one side under heavy braking- so is the side that swings out got an over eager brake or does the other side have a weak one...comparing temps after some long downhill braking loaded heavy it was easy to spot the offender and adjust it. In my case it was one brake not doing enough, 5 minutes under the trailer with a screwdriver through the brake adjusting hole and it was fixed 
There are even some ideas published to check the tread temps across the face of the tire, they should be even, if the center is hotter you may have too much air, if the sides are hotter you may need more air...
There are even some ideas published to check the tread temps across the face of the tire, they should be even, if the center is hotter you may have too much air, if the sides are hotter you may need more air...