According to Wikipedia:
The M48 Patton tank was designed to replace the previous M47 Pattons and M4 Shermans. Although largely resembling the M47, the M48 Patton was a completely new tank design. Some M48A5 models served well into the 1980s with American forces, and many various M48 Patton models remain in service in other countries. The M48 was the last U.S. tank to mount the 90 mm tank gun, with the last model, the M48A5, being upgraded to carry the new standard weapon of the M60, the 105mm gun.
Nearly 12,000 M48s were built from 1952 to 1959. Beginning in 1959, most American M48s were upgraded to the M48A3 model which featured a diesel power plant. M48s with gasoline engines, however, were still in use in the US Army through 1968 and through 1975 by many West German Army units including the 124th Panzer Battalion. By the mid-1990s, the M48s were phased out of U.S. service. Many other countries, however, continued to use the M48 models.