IPF8000s+printing+slow

I have a Canon IPF8000S which has been running smoothly for years. Recently it began working very slowly, especially on photo printouts, regardless whether photopaper, canvas or poster quality. Simple graphics like printing letters on posters prints at normal speed, but at once I print a photo it takes forever. We use mainly Canons "Free Layout " program and printing from CS5. Right printhead replaced in April this year and left printhead replaced last week. What happens is this: after sending photo (not very large file) from "Free Layout" the plotter is "saving" and "HDD" blinking for 2-3 mins, thereafter the printhead takes 2-4 runs over paper, followed by 40-50 secs pause, then again 2-4 runs and so on. During pause the printhead moves abt 10 cm back and forth from home position, maybe 10-11 times. Thus a 50x70 takes close to 1 hour to print, while normal printing time shud be 3-4 mins.

Any ideas please?