Scania 164. 480 problem

chipliner:
Hi , there guys I’m having a little problem with a scania 164. 480. , when the truck is on a steady long pull at around 1400 rev,s there is a little hesitation in the engine , it’s almost as if it’s running out of diesel and the engine runs ruff , engine is fine under normal driving through gears etc and it’s only when on a long pull does this happen , once the revs clear 1400 it’s fine again and will pull right out to the red , anybody got any ideas what might be the problem here ?

Whats this a Scania gone wrong !!! ■■? .