I guess i will have to extend the connection between chip and leds instad, and see if i can reach the total length.
That can lead to problems as well.
See my Hexome project where that happened.http://www.thebox.myzen.co.uk/Hardware/Hexome.html
You could try buffering the signal between each board. Something like a pair of 74LS04 buffers on each board to drive the chip and boost it on to the next distant TLC. You get 6 buffers in one chip but they are inverting buffers so you should be able to cope with the three lines with one 04 per TLC.