It's been about 6 months since I've pulled one off, but I remember having the same issue the first time lol. Don't worry about the insulation, it isn't that expensive (Def. want to take it off first though next time
). Pretty sure part of what is holding it is is glue/sealer, and the rest is it actually being positioned in a tight spot. Start at the corner under the fender pulling and pushing back and forth. You will need to pull that corner towards the front of the car to get it out from under the fender lip. Once that corner and edge is free you should be able to work the rest loose, but you may have to pull the ABS/brake lines out of the way to get it out of there.
Before you drill the holes to mount the pcm, mock it up in there with the plugs plugged in. If you mount it too high it will be difficult to get the plugs on and off due to the filter cap. Also, the next time I do it I will probably not put the large hole in the side for the wires, I will probably open up the bottom and run them up that way instead.
If you still have problems getting it out tomorrow let me know and I will look at it closer when I am back in the shop Monday morning.