Upon completion of training, Overstreet reported to staging battalion at Camp Pendleton, for further assignment to the 1st Military Police Battalion, 3rd Marine Division, Republic of Vietnam. Returning to the states, he was reassigned to the infantry training regiment at Camp Pendleton. He subsequently completed successful tours on the inspector-instructor staff, Wichita, Kansas; recruiting duty in Des Moines, Iowa, and Detroit, Michigan; and finally returned to MCRD San Diego in various drill instructor roles: junior drill instructor, senior drill instructor, series gunnery sergeant, and chief instructor. Reassigned to the Drill Instructor School, he was an instructor, drill master, and chief instructor.
After completing First Sergeant School, Overstreet was assigned to Special Projects at Drill Instructor School, where he undertook the task of completely transferring the Drill Manual onto video tape for a more optimal use during instructional periods. His promotion to first sergeant in February 1979 led to his second assignment on Okinawa as the first sergeant for Headquarters and Service Company, 9th Engineer Support Battalion. Upon his return from overseas, he was the first sergeant of both Companies B and C, 1st Battalion 4th Marines at Marine Corps Air Ground Combat Center Twentynine Palms.
Promoted to sergeant major in October 1983, Overstreet became the inspector sergeant major at MCAGCC Twentynine Palms. Returning to Marine Corps Recruit Depot San Diego, he served as a battalion and regimental sergeant major in the Recruit Training Regiment. Transferring to Marine Corps Base Camp Lejeune, he served as the 6th Marine Regiment's sergeant major. This assignment was followed by duty as sergeant major for the 12th Marine Regiment, on Okinawa. On 6 April 1990, Sergeant Major Overstreet was posted as depot sergeant major at San Diego. In April 1991, he was appointed as the Marine Corps' 12th Sergeant Major, a position he held until his retirement on June 30, 1995.