That points towards an issue either with the cluster or the connection from the engine ECU.But engine right on high rpm. Car starts to stall when accelerating. Maybe I should start with (crank and/or cam sensor)?
The dash is the one major difference between the Catera and Omega, and without seeing behind the cluster there may be additional wiring/plugs for the extra displays/warnings.
I suspect that the alternator only feeds the charge light (and battery voltage gauge), whereas the rpm signal comes from the engine ECU information (crank and/or cam sensor).
If the pedal trick works*, any codes may highlight a discrepancy.
* It should as the car is DBW.
The speedometer issue is almost guaranteed to be unrelated.
Previous owner said that they changed crank sensor from omega.