my first guess would be the linkage. I installed a linkage extension bracket with my lift, and now its hard to get it into 4lo and pops out sometimes. By adjusting where on the bracket the linkage mounts, you can fix it. al least for me.
04' Columbia TJ
33" BFG AT's, OME HD lift, front airbag suspension, teralow 4:1 kit & supershort shaft kit, TW CV shaft, 4.10 gears, JKS body lift, track bars and quicker disconects, Warn 9.5ti, warn front bumper, garvin wilderness rack, and solid cast aluminum tusks,