Sounds electrical to me. If it sounds ok, and if the actual rpms don’t match the tach, then you likely have a ground issue.
If was actually doing what the gauges say, you would hear it. The engine would be running so slowly and rough, and the lifters would chatter. 80’s and 90’s Ford electrical wasn’t the greatest when new. You likely have a loose connection due to the work you did, or even just sitting.....
To be sure, put an aftermarket gauge in. If it stays solid when the factory goes wonky, you know it’s electrical.
If was actually doing what the gauges say, you would hear it. The engine would be running so slowly and rough, and the lifters would chatter. 80’s and 90’s Ford electrical wasn’t the greatest when new. You likely have a loose connection due to the work you did, or even just sitting.....
To be sure, put an aftermarket gauge in. If it stays solid when the factory goes wonky, you know it’s electrical.