On my 2004 FG649, I noticed the other day after driving on the highway for 30 minutes or so that my rear differential was pretty hot. I was able to place my hand on the diff cover and keep it there for maybe 2 or 3 seconds before I had to pull it away. Not the most precise of measures I realize, but nonetheless, does this sound normal-ish? I did just recently drain and fill both diffs, so the oil level is good.