The problem is that anything that chemically removes the paint will also chemically dissolve your plastic. That leaves you with either removing the paint with abrasives (sandpaper) or media blasting You didn't say what the part was so I'm assuming it's an exterior part like a bumper cover for a car. If that's the case and you have a good media-blasting shop close by, I'd have it soda blasted, but make very sure they have experience with plastics. If you choose to sand it, do it by hand and be patient since using power sanders will quickly erase delicate body lines and since the parts are flexy, you can sand "dents" or lows in the part before you know it. So try hand sanding with a block or rubber backing pad, use 180-grit wet and get a comfy stool. Another question is, why strip it completely? If the paint is solid and not flaking off, and it's not too thick, I'd simply scuff it, fill any chips, then prime, scuff and paint.