Its what all us Impala SS owners have to do with our slow belts. They collect dirt and oils over the years and it slows them down. Here's a post I copied from my impala forum.
Something to try and it will only cost you your time.
Try cleaning the belts with hot soapy water - after time the belts tend to hang onto a film of dirt/oils etc. and they don't allow the belt to retract as easy (even if they don't look dirty) - I have used this method and found it to work miracles on a few used cars I have bought over the years.
1. Take the belt in question - (drivers) and pull the seatbelt all the way out so that you can view the entire belt (Do not unbolt anything simply pull the belt as you were going to put it on).
2. Take the hot/warm soapy (regular liquid handsoap) water (no real ratio of soap to water) and dampen a washcloth or and old sock (it should be damp not dripping water so wring it out first) and starting at the portion of the belt closest to the winding mechanism scrub both sides of the belt toward the clasp that locks you into the seat. Once you have reached the clasp - lock the clasp so the belt is unable to retract and allow it to dry in this position for about 10 minutes.
3. Move onto the next belt and by the time you get done with the rest of the them - the driver's belt should be done. Allow the belt to retract and then slowly unwind and then retract the belt into the winding mechanism. You may be surprised by the ease it now retracts.
Check the water to see how much dirt and debris was clinging to your belts in the past 10+ years.
Let us know how it goes - I have a 97 Yukon GT that I picked up used and the PO said that the seatbelts wouldn't retract and that sometimes when he pulled them to buckle up - they would lock up. I said 'no problem' and then proceeded to buy the truck and take it home. I spent about an hour or so cleaning the belts and they all work perfect and have done so for the past 2.5 years.
Just something to try before you replace the costly belts, etc.
