DO NOT USE PAINT STRIPPER!!! Unless you want to buy a new bumper cover.
The only thing to do is to have it media blasted. We've used Tidewater Soda Blasting. Call Robert May at 343-9932. He's super professional and does one hell of a job. He usually does BIG boats, but can do anything. I've had bumpers done before and they come out damn near perfect. AND he comes to you usually.