generally you want to sipe just the centre. the out side tread lugs are not heavily siped because they hold the road as you turn. but siping the centre will help a lot. i have goodyear mt/r tires and i know they suck in mud. so rather then buy new tires i bought a tread groover and just opened up the tread more, lets the mud clear out better. so far after 2 trips to mclean creek it has worked great.havent needed a pull due to stuck tires yet. siping is different, but will help a lot on wet pavement, ice, and rocks off road. may help a little with mud as it will let the tread blocks flex more to release the mud.
either way, goodluck!