If your gauge is climbing that quickly i doubt the shroud is your only culprit, i would still get one but it is not the only thing wrong. I would do like someone above posted and make sure your temp gauge is working (they have digital gauges you just point and click to verify the temp, check the temp in your block) if your gauge is wrong you might not have a problem at all. I would stick with the 180 t-stat because changing to a lower temp t-stat is not going to fix your problem and your engine needs to run at a higher temp to be efficient(you also live somewhere cold 40 deg!!
) I live in Arizona and we are at 105 some days and i still run a 180. Then cycle the air out of your system, get a new cap and a new t-stat and like the other guys said make sure it works before you put it in by testing it on your stove and drill holes in it. Then do a pressure test and verify that you are holding pressure.