1999 3.0L w EST ignition tach rises and fall intermittently

[kramerpage]

This engine WOT is usually at 3800. Recently I noticed the tach displays plus 500 rpm like 4300. Also when going down the river at say 1200 rpm all the sudden it will display 2000 rpm. Engine starts and runs fine. Wondering where to begin looking for this issue. 80 percent of the time the tach displays the correct rpms so Im thinking some connection, ignition coil, gauge itself. and or ground issue. And thats alot of hunting. Thanks for any ideas.

 

[alldodge]

I would say the gauge is going
Put a hand held Tach and compare