Last year my tachometer started to act up over 3300 RPM and would jump around. Now this year my oil pressure gauge is doing the same with the tachometer. Below 3300 RPM both gauges seem OK. All my grounds seem to be ok too.
Anybody have this happen and can steer me in the right direction?

500 EFI Whippled engines - 388 Hustler

This has happened in our current and past boats, one gauge starts acting funny then another. It has been the AGI boxes needed replaced both times. Easy fix plug and play Livorsi Marine Product Index, SmartCraft Gauge Rims, AGI Boxes

VoodooRob - Your issue is Interesting - My 500EFI's have analog gauges - I dont think I have the AGI.

Are you running a mefi 3 ? is it just happening on 1 engine

So do I , AGI converts the signals from digital to analog to use gauges

Here's a pic of the boxes replaced in current boat. If you have Smartcraft and gauges, you have AGI boxes, usually under the dash. Notice the gauges it affects, the same ones your indicating trouble with. If one is acting up the other is right behind it, replace both of them. If you have 500EFI they run on MEFI3, correct? I do not know 100% if 500EFI run on the Smartcraft system. Maybe F2 Speedy Knows or someone else will chime in?

Ya, Rob.....if its stock it will be a MEFI 3 no smart craft, your 600 SCI's are probably running the PCM 555 controller ?

Yes on my 600SCI F2 Speedy. I don't know too much about the 500EFI but do know they run the MEFI 3. Thanks for the info on that system not being Smartcraft.
To the OP, now you have to chase grounds start at the big ones and work your way down. Maybe BUP will chime in, with some tips.

Yes MEFI 3