Generally, W-2 statements reflects taxable earnings while the check stubs and last pay statements reflect total earnings.
To convert from total earnings to taxable earnings, you need to subtract the nontaxable deductions, including parking deductions, FSA deductions (medical and dental deductions, flexible spending account deductions, and dependent care deductions) and retirement deductions (403(b), 457). These deductions are typically itemized in boxes 12, 13, and 14 of the W-2.