we have a '04 RR with 68k miles. The last 2 days we have gone over mountain passes in Utah and when going down the truck wants to stay in the lower gear even when going on a flat valley floor. The problem goes away when we shut it off for a few hours and works fine going around town. First time we have had this issue. Any ideas or suggestions will be much appreciated.

Also, when going briskly around a turn the left front occasionally has a clunk sounding as if something is momentary binding ....what could that be???

thanks again to all for your help.