Gas Guage reads full all the time. Boost Guage reads high. Engine idle speed in neutral is around 1800 rpms. Highway driving seems normal. Starts hard...thanks for your help.

That gen of Bonneville is notorious for failed stepper motors in the clusters. Causes the gauges to take on a mind of their own when they fail. It would be good to confirm the cluster readings are accurate, and rule that out as an issue.

What codes is it setting?

Don't know codes yet. Only abnormal engine symptom is high idle speed. Suspect that whatever is causing the Guage to be wrong is also causing high idle speed.....