When you did the clutch replacement, was there oil in the bellhousing? If so, then you either have a leaky rear main seal, or a leaky input shaft seal in your transmission. If any type of oil gets on your clutch disk, it will slip. You can try bleeding the clutch and adjusting the pedal if you feel that it is not completely disengauging (try that first). I would guess though that oil is getting in your bellhousing which is what made the original clutch slip in the first place.