Truck shut down .

I started experiencing issue at night couple weeks ago , while I was sleeping truck did shot down . Started right away after . Sometimes it drops rpm like it's going to shut down but after come back to 700rpm at idl back . During first night shut down happened 3 times and rpm dropped about 3-4 times . While driving - now issues at all . Week later same issue during idling at the auction . Several times , I tried to raise rpm to 1000 - seems ok , one time happened on the road already during driving . Finally I swapped ecm to see if that the problem , no issues for 2 days ...now again

 

It's 3406e 2000 379 peterbilt

 

No flickers ...have cel but that's due to barrometric pressure sensor

 

How to check air in the fuel issue ?

 

...just replaced that fuel line ...maybe didn't tight enough ....((

 

I broke the fitting in the back of the ingine due to the first time doing it on the road and after installing didn't apply any Teflon or something on the fitting to make sure it's tight (