Slow printing from DOS

I have a client that has a computer that has Windows 2000 on it. They lease it for a specific application. We connected it to their network, loaded their DOS based software and all works good. The problem is that when printing to a dotmatrix printer on LPT1 it prints about half the document then seems to slow down for 2 or 3 lines the starts going fast again. Takes 30 to forty seconds to print a form (just filling in the blanks on a preprint). Can’t seem to find any settings to affect it in any way. Any ideas would be appreciated.