Machined and black will also damage in salt. I would just stick with the OEM 20" wheels. They look good, and you'll save yourself the trouble of learning the hard way.

 

I believe the stock 20 inch wheels on the 2009/10 are 8.5 inches wide with a +44 mm offset. They are 6X135 bolt pattern and hubcentric. The wheel shop that I bought my wheels from had a chart with the recommended wheel sizing and specificaitons. If I remember correctly they recommended a +35 mm to +44 mm offset with a 20 inch wheel or larger. Always get a hubcentric wheel or one that comes with hubcentric rings. This will help with vibrations. With the above offset your truck will handle properly. To many people put the wrong offset wheel on their trucks and they handle like *****. Don't ask how I know! The offset and width is very important and as close to stock will work the best.