I have found that:

Dry ice works very well on flat panels where there is a big sheet of the mat that can expand/contract against the sheet metal. Floorpans are a prime example. A tap with the hammer will usually shatter it and it comes right up.

Dry ice does not work well on smaller surfaces where the mat is more rigid and the sheet metal is also more rigid. Specific examples like door seams, A-pillars etc. Ive found a heat gun is the way to go there. Mineral spirits to clean up afterwards, or perhaps a flapper/wire wheel if youre painting.

 

I just did my 99 and used a heat gun with a 1" wood chisel turned flat side down. The secret was to get an area started but not to over heat it as that would make it to gooie. Just heat it enough to get the chisel moving easily and once you get the area heated the heat kinda keeps heating the surrounding area ahead of you so it goes pretty fast, then clean the risidue with mineral spirits or laquer thinner. Took about 45 mins. each side. There was about 3# each side.