LoooSeR; good question...first of all, it was right in the middle of the two most significant Soviet Army events of the 1960s: exercise Dnepr in 1967 and Operation Danube (the invasion of Czechoslovakia), in 1968. These two events shaped the Soviet Army of the Cold War and provided very real rehearsals for WWIII. You're correct, the SU-122-54 was the product of the Soviet Army experience in WWII...especially during the Manchuria campaign against the Japanese. The Soviets developed tactics for combined-arms organizations known as "Assault Groups," "Storm Teams," and "Forward Detachments," with assault guns/tank destroyers at their core. After the war, the SU-122-54 (probably known as the SU-122 (M1954) by the Soviets), was secretly fielded in companies/batteries that were organic to select/high-priority MRRs and TRs. As mentioned above, the SU-122-54 was deployed for both Dnepr and Operation Danube.
Since it wasn't forward deployed in the Groups, it was almost missed by Western intelligence through it's development, short life, and death (at Khrushchev's hand...guns bad, missiles good). The first mention of the SU-122-54 in an official US military reference manual was in a USMC MCIA manual in 1996...that's 41 years after it was fielded by the Soviet Army. There was limited intel available on this vehicle as early as 1958 but most of it was Top Secret so it didn't reach many folks in the field. The CIA gave it the designation SU-100 (M1968).
I could go on...the SU-122-54 truly made the D-25 122mm main gun (versioned for the SU-122-54 as the D-49), what it was meant to be...etc.