i have a 01 2wd supercrew 4.6 with 208k and when you step on it at about 3500 rpms the battery light flashes and when it shifts out of first gear when you do that the belt squeels. if you keep it under 3500 rpm it never comes on. does anyone have any idea what it could be?

 

The alternator needS to be replaced due to worn brushes and comutator.
Belt needs to be replaced due to slipping.
The reason the belt slips is the large difference in engine RPM when a shift occurs and the large drop in all the driven parts off the belt, that have to slow down as well.
If the alternator bearings are rough, it will add to the belt load.

 

yup, alternator and belt, do them both before you get stranded.

wouldnt hurt to do a battery test as well since you are putting more strain on the battery with a weakened alternator

 

ok because i tested the alternator when the engine was idling and it was reading fine. it has a dura junk alternator and a crap walmart battery in it when i bought it.

 

yea mine did the exact same thang except the belt, so I had to buy tht alternator, but if u dnt get everthang right it will cut off on ya and bout cause a wreck, I learned the hard way... check the battery cables close.

 

mine did this too. changed out the alternator and a new belt and all is good

 

well i work at a parts store so as soon as i get some extra cash im going to get it. i have been replacing all kinds of stuff on this truck. never ending

 

You should change your tensioner along with your belt. its only like 40 bucks.