injection pump/deisal

hey everyone
my bro has a 1994 cummins turbo deisal 5.9
it's 1 of his work trucks.it has been really slow lately,and someone told him that it might be the injection pump.
is there a screen or a filter inside the injection pumps that need to be clean or replaced

thanks for any info

I might not be the injection pump. If the truck is turbo then there could be a hole in the air charge cooler or one of the pipes going to it. we see this alot at work when people complain of low power and I don't think that there is a screeen on the pump itself but the fuel filter is right there and that migh need to be changed. hope this welps if need anything let me know