When I did mine, it came off easily. It 'snaps' into place with some sort of clasps, and pull away from the pilar and it pops right out. Once you see the backside it will be obvious how it works. The new pod piggybacks ontop of the OEM and both are snaped back on the pilar.
I had the 'tweeter' so I had to do some carving to the OEM, but that gave me a hole to run the wires thru.
I didn't didn't have to pop off the weatherstriping. That may be a good method, but I can't imagine the plastic pilar post coming off any easier than it did for me. Too easily. I worried that the integrity had been comprimised, but everything has been AOK for a long time. Love the unit!!!!
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2001. 5 2500 SLT+, QC/LB 4x4, ETH, 6spd, 3:54 LSD, camper/tow equip. , NV241HD, Bright Silver, Snug Top, Ispro w/3 pod pillar w/tweeter, Pyro, Boost & Mag Hytec cover w/temp guage, "Plain Wrap" (no decals or emblems)