Received a W2 from DFAS which I had filed and 4 days later they send me another W2 (with a "P" code in box 12). Is this non-taxable or should I file an 1040X amended form

Code P in box 12 of your W-2 indicates you have moving expenses.  I recommend you calculate an amended return; if you are in military service (the W-2 from DFAS indicates that you are), you are still entitled to deduct the costs of moving on your return per the Tax Cuts and Jobs Act of 2017, net of any reimbursements.  I have included a link to the IRS Publication 521 on Moving Expenses below.

Thank you for your service.

Moving Expenses

Thank you for your help

My pleasure.  🙂