Nozzle touching the object after going up 5mm

I'm having this print issue with z travel or layer height. It prints fine for the first couple of layers, but as it go up in layer, the nozzle starts to get closer to the printed object and after the z axis going up 5mm, the nozzle starts to touch on the object and melting it. At first, I thought my z travel is not accurate, but after checking the calibration, the z travel is within 0.02 mm. I don't know what could be causing this. Can someone give me some suggestions on what to check. I'm using sprinter and slic3r. My layer height in slic3r is 0.3mm seem to be normal for a 0.5mm nozzle. Help!
Thanks.

It sounds like you are extruding to much plastic and it is accumulating as the layers go up. Reduce the extrusion multiplier until you get the correct amount of plastic.

To test you can slice a cube with 100% infill and reduce the extrusion multiplier until you see gaps in the infill, then increase the multiplier until the infill touches and forms a perfect solid layer and that should be the perfect setting.

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Thanks for the reply. I've tried extruding less plastic, but doesn't seem to be the porblem. I started to see gaps after changing to extrude less plastic. The first layer looks good with my original settings, just that the z is not moving correctly when printing, I'm guessing because I calibrate it using pronterface, but when printing, sprinter has it's own speed, and maybe my motor can't handle that speed. I need to go back to sprinter and see where I can change the speed for z. I hope this is the reason.

Maybe your z-steps are not high enough ? did you calibrate the steps in the firmware ?

Calibrate all of your axis and your e-steps/mm. you'll know you are extruding the right amount of plastic when the top layer of parts are 98-100% full but not bulging.

too little is better than too much.