these have popped up and im wondering what could be causing them, what needs to be done to fix it, and about how much for each.

1. P0521 Engine oil pressure sensor/switch circuit range/performance. Oil changed regularly and checked oil level upon this coming up and was normal.

2. P0654 Engine RPM output circuit.

3. P0856 Traction Control input signal. (possibly related to number 4)

4. U1040 Loss of communication with Brake/Traction Control Module. (possibly related to number 3)
*Also the DIC shows Service Traction control/Stability control, Service Brake system, Service ABS system intermittently, and sometimes just traction control/stability control is off, others nothing at all. Wonder if this is related to the bad ground as stated in a similar post?*

P0521 is the only one turning on the SEL, the other 3 are in the history.

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HID's(8000K Dims),K&N Air Charger,LED tailights,STB's F&R with Don's brackets,Custom Catback.

#1 is most likely the oil pressure sending unit, as for the other ones I'd agree with a bad ground somewhere.