I noticed on a road trip that I couldn't get the headlights to go to high beam. When I pull the signal light lever back to switch to high beams, the high beams come on, and the indicator shows High Beam, but when I release the lever, the lights go back to low beam, along with the indicator.

The problem is not constant. After the vehicle has been off overnight, the lights work normally, but after I've been on the road for awhile, the problem returns.

[UPDATE several years later for someone who might stumble across this] I am embarrassed to say that I think the problem was that I didn't have the headlights turned on. The daytime driving lights were enough to make me think the headlights were on. Each time this happened on a road trip, the trip started in daylight and progressed into darkness. Once I realized this possibility, every time I've noticed this problem, I find that I've forgotten to turn the lights on.

Any ideas?

 

probably the multi function switch.

 

I would agree with jkeaton on the switch. As you know(or at least it works this way on my 05) a light pull on the stalk will allow a quick flash of high beams and goes back to low when you let go. Pull the stalk all the way and it will "click" and the highs will stay on.
So, by that logic, something is either not allowing you to pull all the way, or the switch is not holding the click position.