1998 freightliner has a n-11 cutting out while driving.

Could be a fuel filter nearly clogged, I have a 96 international with a m11 and mine cuts out when the fuel filter needs changing

 

The fuel runs through a fuel warmer behind the ecm. The cores catch all the trash and cause it to act like you describe. Usually the fuel lines are long enuff to eliminate it from system to see if it clears the problem. If so back flushing it works wonders. I would only bypass it a short time to test it.

 

my 1997 freightliner with a m11 did this turned out to be the ecm going bad it was derating...put a new ecm in it never did it again...if that's the case make sure they get your specs and stuff out your old ecm and put the new ecm back the same way...cummins atlantic in nc did mines and did not get the program out the old ecm and now the trucks stills runs great and gets about 6.5/7 mpg but is not as fast or pull as it did before..then they wanted to charge me again to fix what they messed up..lol not happening..but I hope that's not your case ..cost me 2800.00 back 4 years ago...im sure you can get them somewhere cheaper but I needed to get back to work so I did ..lol