Don't know what year truck you have, but I have the 4" Turbo Back aluminzed system on my truck with a polished 5" tip. It's holding up fine (corrosion wise), but I live far away from the sea shore.
I have been happy with mine with the exception that there is the draeded drone at 2100 rpm when pulling the trailer under heavy throttle.
Some people get the drone, some don't. I got it. It's not so bad that I'm going to change out mufflers, but it does take a little getting used to it. There is no drone when not pulling the trailer.
Good system. It took longer to pull/cut out the old stock system tahn it did t install the new one.
Juan