Half a tank blues

Anyone with first hand experience with this please speak. 2008 6.7 full delete mild EFI tune (80k since The D and tune. And has been running great since the tune and D now has 255k total. Well this week I done a east to west run and after the 4th fuell filter I come to realize it was doing after a half a tank only,new filter or not. Cutting out,no power and lots of black smoke,the emptier it gets the worse it gets. If I keep it at half a tank or more pulls like a train!! Wth ?

 

No the fuel supply and filters are all stock. Will check the vent out today.

 

It started in Knoxville tn and did that all the way to southerner Cali and back,5000 + miles and five filters. I'm about to drop the tank as we speak,iv been told half a dozen times its only pickup tube broken or has a hole in it. I'll know in a hour.

 

Really? ...

 

i said full delete from the very beginning(you even highlighted it for me). But the fuel supply is all factory. it was a bad fuel cap believe it or not,was about to drop the tank when I read the cap vent could be stopped up so I took it off drove to parts store and has been running great since.