My headlights dim when i roll my windows up or down. Ive replaced the battery. I think its the alternator not supplying enough power fast enough??

You are probably correct. Have alternator checked, if you are a do it yourself guy, it should show 12 to 13 volts running and checking amperage output depends on what the alternator is rated, probably in the 60 amp or so category, but that's a bit more difficult to check

Get yourself one of those cigarette lighter digital voltage testers. With the truck running you should have around 14 volts. With the truck off should have min of 12.5. Then run the window up and down and watch the meter. It should not vary more than a few tenths of a volt when running window up and down.

Turn on your car's engine and let it idle. Don't have turned on such as lights and air-conditioning as you need to check the minimum alternator ampere output. Use a multimeter and set it to read amperes. Put the metal prong on the end of the black wire that extends from the multimeter onto the negative battery terminal. The negative battery terminal has a black cable attached to it and is labeled "Neg." Put the metal prong on the end of the red wire onto the positive terminal of the battery. The positive terminal has a red cable attached to it and is labeled "Pos." Read more: How to Check Alternator Amp Output | eHow.com http://www.ehow.com/how_7673351_check-alternator-amp-output.html#ixzz2IRAbbxOd

I'm having the same kind of problems but I changed the alternator and the battery. It got better for about 6 months now it's happening again help