This is a very strange electrical problem. I actually have the opposite problem of most people. When I crank the truck for the first time in the morning it cranks great but as I drive it the battery runs down (or so it seems) and when I try to crank it after a 15 min or so trip it will hardly turn the starter over. I have a 105 amp alternator that is new and tested good as well as a 8 month old red top that also tested good. I am really not sure what to do with this or how to diagnose this problem.

I am running an electric fuel pump (hollie blue) as well as LS1 fans. I have had this setup for a while with no problems until lately.

 

How old is the starter?

 

about 2 years or so.

 

So if you wait awhile and try and start it after a couple of hours does it do fine?

 

Sounds like a starter problem. A starter that is going out will drag or be weak when it heat soaks, like when you mentioned the truck sitting about 15 minutes then not wanting to crank.

 

It was the starter. I went out and bought a nice mini starter and boy was that a pain in the ***! I shimmed that thing for 2 days and it still hung up. So now I am sporting a nice new orileys reman.