This is not a new problem, just one I haven't figured out.
The passenger side floor board, specifically by the tranny tunnel gets really hot after an hour or two of highway driving.
I've put some aluminum heatshield stuff from J.C. Whitney there,(aluminum side down per instructions), it helped a little.
My 5 spd tranny/t-case are both full of fluid, engine doesn't run hot, and it looks like I have the heat shields on the underside.
Anyone seen this or have a fix?
Thanks,

 

Tranny tunnel...hours of highway driving...you do the math lol. Transmissions can get really hot, especially autos. If it's REALLY that hot, I would install a trans cooler (they are around 80$ for Pep Boys, more for a TRD unit that includes brackets) and get your trans checked out ot make sure it's not wrecked yet. Change the fluid as well.

 

Are you sure it's radiating from the tranny tunnel?

My 2nd gen pickup used to have a hot passenger floor too. I didn't notice it normally, but only after I was driving around with my carpet out.
Have a look under your vehicle, as you might find the exhaust runs down that side

So that I didn't melt all the sound deadening I was going to do, I installed some heatshielding onto the exhaust itself. It's just some 3" steel pipe cut in half and tack welded along the top of the exhaust.

Dave.

 

His tranny is a 5 speed so no cooler. Hehe - our passenger side is on the opposite side of the exhaust.

You should be able to put your hand on the tranny/transfer case after they've been driven around. Too hot and there is something definately wrong. Only suggestion I have is that synthetic gear oil helps lubrication and may help lowr temps.

 

I'm not suggesting anything, but I'll share an experience with another car I had. The exhaust was on the passenger side, and it began to get extremely hot. I took it in and it was the pre-cat on the car causing the heat. Of course instead of getting it replaced. I instead got rid of it, and replaced it with a down pipe. Problem solved, plus added a few horses. I hope that helps. Best of luck with figuring it out.