If i recall correctly the sensor for the temp is located just inside the grill, therefore when standing still the heat buildup from the engine and raod wiill reflect a higher temp. ( For ex. last week in a couple weeks ago in denver it was 95 deg outside and while driving the gauge showed 95. When stopped at a light the guage showed 115deg. (thank God for the inventor of air conditioning!)
As far as the altimeter <img src="/forums/images/graemlins/confused.gif" alt="" /> possibly changes in baraometric pressure? Just a wild <img src="/forums/images/graemlins/butwiggle.gif" alt="" /> guess. Have you checked your manual to see if the altimeter needs to ba calibrated? I know the compass needs to be calibrated (a series of turns in specific directions on flat ground away from metal).

On the side, my favorite weather forcaster "Les Nesman on WKRP"
Andy: "Les what exactly is your eyewitness weather report?"
Les: "I look out the window and say "It's raining a little on the west but the south side is nice and sunny"