I have a 2003 chevy silverado 1500 5.3L and every time I go to start it, its dead. I have a brand new alternator and battery. Once I get a boost it'll start and if I shut it off and immediately start it, it will start, but after a few minutes it won't. I know something is drawing power because I unhooked the ground cable to the battery and hooked up a multimeter and it would read almost 5 amps. I tried checking all the fuses but it would be dead before I could do them all. Does anyone know what this could be?

 

Welcome to the forum...
You're on the right track putting a meter in-line to check current draw...
Do you have heated seats?
Anything plugged into the 12v outlets?
Rear Seat Entertainment (DVD player)?
Extra audio equipment like an AMP?

The key in accessory mode will draw about 5 amps....

 

For the fuses, pick up a self contained fuse tester. They are inexpensive and indispensable, you won't need to have power in the truck to test fuses with it. I got one in a $20 fuse pack. A fuse pack like this one

Also, I know you said you have a brand new alternator but take it down and have it tested, there have been a few occasions where I have gotten faulty alternators that simply did not work straight out of the box.

Hell, take both the alternator and battery down to Auto Zone or where ever you have and get them both tested just to be thorough.

 

Ok the battery wouldn't hold a charge so I got a new one but something is still drawing more power than it's suppose to