car not de-revving smoothly?

hi guys. sorry this is a repost from subaru section didnt see this section before i posted over there tho :)

i have a 02 impreza GX with 60,000km when i accelerate then take my foot off the gas the car will shudder and be jerky for a second or 2 until the revs drop down. most noticable in first in bad traffic. so i take off, rev to 3-4000 then release the accelerator and the car wont de-rev slowly until after 2 or 3 seconds.

any idea what this could be?
thanks so much!