I did it this way a few months ago on some 5% tint that some xxxx had put on, took about an hour all up & cost about $5 for the cloudy ammonia & black bags, I didn't even need the razor except to get it started, came off as clean as a whistle.

http://www.tintdude.com/remove.html

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Beaten up old 98 Gen 2 Liberty, 13.0, stock V3 STI running gear.
07 Transit motor home
69 VF & 70 VG Valiants needing full restoration
Yamaha Zooma 50cc rocket hopefully going with the Transit.