Rough running durring acceleration

[AJL521@xxxx]

Hello,

Latley I've been driving my D every day, with this nice summer weather we're 
having in Chicago, and I've noticed a problem, Durring acceleration if the 
pedal is more then halfway to the floor, the engine boggs out, and runs 
extreamly rough, This problem gets much worse when the headlights and 
cooling fans are on. I think the problem could be caused by a weak Duciller 
alternator, or a combanation of bad settings, possably timing or air fuel 
mixture. I also thought that the catilitic converter may be plugged.

The muffler is going out, but Im not sure if that could contrubute to the 
problem, looks like I get to look for a new muffler now.

Any ideas would be appreciated
Andrew

vin 4194