No.  In order to meet the "last 60 months in covered employment" exemption, an individual must work his or her last 60 months of employment in a position that is covered both by Social Security and the same retirement system the pension is based on.  (Under some circumstances, the 60 months can be reduced for workers who retire before March 2, 2009.)  In addition, the Social Security-covered earnings from these last 60 months of employment must be "considered" when determining the pension amount.  TRS and DROP are separate pension systems, and the earnings of an employee while participating in DROP are not "considered" in computing the individual's TRS pension.  Therefore, employment while participating in DROP can not be counted toward the 60 months needed to meet the "last 60 months in covered employment" GPO exemption for a TRS pension.
 
NOTE:  The Social Security Protection Act of 2004 (P.L. 108-203, enacted March 2, 2004), replaced the "last day" exemption to the GPO with a requirement that the person work in a position covered by Social Security for the last 60 months of government employment prior to retirement.  For more details on the change in the law, see the question on the Social Security Protection Act of 2004.