Slipping seat-post

I recently got a new 20" Torker DX (well, new to me) uni on e-bay. It definitely it allot better than my 24 for freestyle and trials. Well anywho, as I ride, I can tell my seat post is slipping. After about 1 mile the post has slid down by about 2 inches. I tightened it down really well. Any suggestions for fixing this?

you could try a shim…other than that id recomend maybe a new seatpost clemp…somethin real tight like a 3 bolt…im not sure which one comes with the new dx.

Here is a related thread that I remember from a while back. If your uni has a quick-release clamp, replacing it with a regular clamp solves most seat twisting and slipping problems, assuming the seatpost is the right diameter for the frame tube.

Tigten the bolts more?