The plate is a heat shield. If you look though the holes on it you should see a crack on the cast piece behind it. The cracks I have seen usually are noticable though the hole. It will sound like a tapping noise that may go away when it gets warm. The Stock replacement is like 200 or so. It will happen again as toyota has not fixed the problem. Nor do they acknoledge it is there fault. In actuallity the design made this part of the manifold thin and weak. Over time it cracks.
I personally recomend buying LCE Headers as they are 50 State legal, come with all necessary gaskets, and in your truck, are mostly bolt in. They are a tight fit, but require little mod. If I remember correctly you remove a hanger attached to the bellhousing. And with some cursing you'll get it in. However I recomend fabricating some heat shields to cover the brake lines on that side, as well as relocating the oil filter with an available kit. You wont be able to get to the filter as easy and it sits 1/4" away causing it to met the cover/paint. You will notice an improvement in torque and throttle response when coupled with an intake. They sell for about 100 more than the OEM part. Other companies make good ones also,but may not be 50 state, or are not as well built.
I think you need a 5 speed too, I don't think you can get a set for an auto trans. Hope this helps. Try a search on Yahoo for TACOMA HEADERS 2.7
