Burnt smell from the engine compartment

My truck is an 06 2.7l 5 speed and just rolled over 60,000. Lately, like the last 2 weeks and after a long trip, I have been smelling a burnt smell when I get out of my truck. Not sure what kind of burnt smell it is. I have checked all 4 rims and they are cool so its not brakes hanging up. Checked fluid levels and all seem fine. Just did diff and tranny fluids changes. Haven't found any leaks. Unfortunately I never get a chance to inspect it during the day, only at night when I get home from work. Just wondering if anybody had a mysterious smell and found the problem or somebody has more ideas as to where to check. Oh and it tracks staright in 2wd and 4wd under acceleration, so don't think bearing or CV either.

 

Sounds like you could be burning some kind of oil.
The only thing I can tell you is to get a good light and look for anything wet or greasey.