This is a real Soviet made ZSU-23-4 Self Propelled anti-aircraft gun. Photo via U.S. Army.
The U.S. Army began reducing its inventory of M551 Sheridans in 1978, remaining Sheridans were relegated to the role of ‘bad guy’ for war games, being modified to look like various types of Soviet tanks for use on the U.S. Army’s then new National Training Center, in the early 1980s.
Two Sheridan ‘fake-news’ ZSU-23-4, National Training Center-Fort Irwin, California, September 1982. U.S. Army photo by Ben Andrade.
NTC, California. USA photo.
Photo attributed to Stefanowicz.
A ‘ZSU-23-4’ spotted in a convoy of fake-news Sheridans, National Training Center-Fort Irwin, California, January 1986. U.S. Army photo.
A 177th Armored Brigade ZSU-23-4- M551 Sheridan, parked next to a real BTR, NTC-Fort Irwin, California, March 1988. USA photo.
I remember when I was part of the 1st/185th Armor, CSC Company (armory in Apple Valley, later becoming Delta Company) of the California Army National Guard, we routinely used Fort Irwin for weekend drills. In the early 1980s, NTC was literally a dust bowl with almost no facilities, we used the giant boulders as our targets for live-fire tank gunnery. 
Finally, in 2003/2004 the M551 was retired from the OpFor (Opposition Forces) role, with the very last Sheridan seen being hauled to the U.S. Navy’s China Lake in March 2004 (probably to be used as a target).
Parked inside the Opposition Force’s (OpFor) vehicle compound, NTC, California, January 1991. USA photo.
In the last decade of the use of Sheridans as ‘Krasnovian’ OpFor vehicles, the M551s were kept alive by cannibalizing parts from other M551s, and the unusable parts were sold as scrap. My last encounter with the Krasnovians was in 1998, with the Idaho Army National Guard.
Cold War Armor: 
M551 SHERIDAN, PROPAGANDA BORDER GUARD
Vehicle I-D: 
MORE U.S. ARMY FAKE-NEWS TANKS, TIGER STRIPES ANYBODY?