This morning I turned my truck on and gauges didn't work. They started working when I revved it. Then I noticed my voltage was at 9 volts when driving. I went home and and removed my battery while truck was running and the truck turns off at 4000 rpm. I reinstalled battery and volts at startup are at 13.5 but drop as rpm goes up. This started happening when I left my stereo on for a few hours and had to jumpstart the truck.

 

did I read that right.....volts DROP with RPM INCREASE?

 

sounds like the alt. to me. no reason for the truck to die once it's running already unless the alt. is bad.
At least in most cases.....

 

jumping cars isnt as easy as it used to be.. when your battery gave out from the radio being on you got a jump which could have fried your alt. it happened to a buddy of mine only in reverse order, he gave some1 a jump and it ended up killing his alternator which took his battery out as well.

take both your battery and alt to an autoparts store and have them both checked out just in case.. see where you stand from there

 

Thanks. I'll take the battery off today and then the alt tomorrow.

 

sounds like an alt. if it is a charging problem with it running.

 

The battery and ALT tested out ok. I didn't think they spun the alt enough during test so I installed the stock and it fixed the problem. Now I have a 145 amp that's only good to 3000 rpm. Is there anyplace that can fix them? A new one was $250.

 

Found this one, it's at least worth giving a call.

http://www.texasindustrialelectric.com/home.asp

 

should be able to take that to a place that rebuilds alts and have it fixed for cheaper than a new one.