I recently bought a used GT STS frame. I believe it is a 1998 GT STS 1500 DS. The information I have found various places online http://www.epinions.com/bike-Bicycle..._1500_DS__1998 indicates this bicycle takes a 31.6mm diameter seatpost.

The bike I bought had a 31.6 Thompson Elite seatpost which was jammed in the seat tube. After great effort I got it out and found that it had evidentally been overtightened causing it to bulge out then the bulged area later forced down into the seat tube causing it to be stuck.

I have another 31.6 post from my Klein and although it slides smoothly in the Klein it will go into the STS but it seems to require an excessive amount of force.

My questions:
Can anyone verify that 31.6 mm is the correct size for this bike? I seem to find it consistently in my searches but it seems slightly too large.

If 31.6 is correct, what is my best option to use the post without having to twist / force it up and down? (the seat tube has already been cleaned thoroughly and the post greased, and I'm not trying to force it past the seat lug and into the curved area of the seat tube)

Thanks for any help folks can provide.