Tachometer showing 100-200 RPM at idle..Bounces around at hwy speed.

Replaced entire gauge cluster at a cost of over $500, 6 months later problem resurfaced - mechanic called Chrysler and was told this is a known problem and that they had no permanent solution - all they could say was replace the gauge cluster again and cross your fingers - at $500+ a pop this shouldn't be happening!

Original tachometer replaced on 5/29/2012, problem occured again on 3/18/2014 - informed by Dodge that part warranteed now for only one year as they continue to have problems with tachometers.

1) Why isn't the warranty for this part longer and 2) why would anyone replace it twice knowing that it would fail again (according to the dealer)?