since 2003 i changed many light bulbs for my 2003 tahoe headlight.
sometimes it goes out in a week..
i tried sylvana, eurodezign, and many other brands..
the longest one was called sylvana.. longlife...something..
it lasted for 6months i think...
i saw many chevy vehicle with one daylight on..and many with one headlight on too..
is it normal that the light bulbs go out that fast?

 

Welcome to the forum.

Check your voltage while driving w/ lites on. Also check the socket to ensure that there's no corrosion.

 

i checked the voltage...and it goes up and down...why is it doing that..?

 

the regulator in the alternator my be bad or going bad...
most of the time its easier to replace the whole alternator but you may be able to get a rebuild kit that includes diode, regulator, new bearings at about the quarter of the cost but it can be a little bit of work...

check all your battery cables for good clean solid connections at all points