Crankshaft Position Sensor 2.5L $26.54
It does not look to hard to replace. It is located near the crank shaft on the radiator side. You just need to unplug it and remove two bolts, slip in the new one rebolt it and plug it in and you are done.
All Tachs get their info from the CKP sensor. It is a common problem with SHOs and your description of the problem sounds exactly the same.
