Have a 2004 chev 3500 duramax diesel with 250000 miles. Use the truck everyday! Tach is stuck at 5000. Speedometer varies crazily. Engine idles rough when braked at stoplight or in park!! Was told some pressure switch was shot!! Looking for help on how to fix it!!

 

the tach and speedo is more than likely a bad cluster, they can be sent off and rebuilt. The idle could be the fuel press. regulator in the cp3 pump. Also would check that fuel rail press. sensor is reading normal.