Thanks lagbolt,
figured it out before I saw your post. This seems to work:
=IIf([tmpyrssvc]<=4,[tmpyrssvc],IIf([tmpyrssvc]>DMax("years","tblpay","[grade]=forms!frmpersonnel!tmpgrade"),DMax("years","tblpay","[grade]=forms!frmpersonnel!tmpgrade"),IIf([tmpeven]=1,[tmpyrssvc]-1,[tmpyrssvc])))