My friend has an 05 hemi magnum running poorly. I have not had a chance to drive it yet but he described it as a misfire. I was able to pull these codes.
P1521/ "not sure what this is"
P0300/ multiple Cyl. misfire
P0355/ crank Pos. sensor Circ.
P3015/crank Pos. sys. variation not learned
I'm guessing the crank position sensor may be bad but I am unsure if that's the problem or if there may be other problems.
Any help or advice would be greatly appreciated.

P1521–INCORRECT ENGINE OIL TYPE

When Monitored: Engine Running.
Set Condition: Using the oil pressure, oil temperature and other vital engine inputs the PCM can determine the engine oil viscosity. Incorrect viscosity will effect the operation of the MDS by delaying cylinder activation .

Possible Causes INCORRECT ENGINEOIL TYPE ENGINE OIL CONTAMINATION ENGINE OIL
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding.
Diagnostic Test

1. ACTIVE DTC
NOTE: Review the customers oil change history. Ensure the customers is using the correct engine oil viscosity. If the incorrect oil is being used, change the oil, using the correct engine oil viscosity.
Ignition on, engine off.
With the scan tool, read DTCs.
Is the DTC active at this time?

Yes

Go to 2

No

Test Complete.

2. ENGINE OIL
NOTE: If set along with P1521, repair any engine oil pressure or temperature DTCs first before continuing.

The following conditions must be checked.

OEM recommended oil viscosity is being used.
Customer is following the oil change schedule.
Check the engine oil for contamination. (i.e., fuel and/or engine coolant)
Internal engine condition that may effect oil pressure.

Were any of the above conditions found?

Yes

Repair as necessary.
Perform the POWERTRAIN VERIFICATION TEST.

No

Change the engine oil using the correct oil viscosity.
Perform the POWERTRAIN VERIFICATION TEST.

If this was an early production vehicle I'd say check with a dealer on a TSB that was issued for this. But since you just had the engine rebuilt I suggest that you:

1. Verify oil viscosity used.
2. If incorrect oil was used, drain and refill with proper weight oil.
3. Insure that your oil pressure sensor has not been damaged during the repair work.

I don't think he has had an oil change in a while, should be an easy fix for that. My main concern is whether replacing the crank sensor will be sufficient or if there are other issues.

Duuno, my SIL had an issue with his '10 Ram and wrong oil was one of the codes, with several VVT related codes as well. Dealership wanted to bend him over for new VVT stuff to teh tune of $1200.

We changed the oil per the TSB that addresses these codes and viola it was all good.

Apparently, these engines are very sensitive to oil viscosity and old oil gets thicker.

I would start there myself, probably needs it anyway.