[Vespers War]

The v2 Soviet Vehicle Guide mentions the M4 Sherman's continued service in Yugoslavia, but during its historical breakup both M18 Hellcat and M36 Jackson tank destroyers saw combat use. Both vehicles were serving with the TOs (Territorial Forces) of Yugoslavia's constituent Republics rather than the main army, but would likely show up in Twilight War scenarios (as would the M4s that had been assigned to Jackson units as driver trainers). Their role had shifted over time from anti-armor use to infantry fire support, and the Hellcat's ammo loads reflected that - in the 1950s, they carried 15 HE, 18 AP, and 12 HVAP rounds. In 1990, the standard load was 23 HE, 4 AP, and 18 HEAT rounds.

When Serbia finally retired them in 2005, there were still 203 in service. At least some had their 450 hp Ford GAA gasoline engines replaced by 500 hp diesels, either late V-2 from the T-34 or the V-55 from the T-55. I've seen photographs of one with a V-55, and it's possible the V-2 reports are confusion with Yugoslavia's efforts to re-engine their Shermans, but it's also possible they used both engines in Jackson upgrades.

Edit: I misread my source. Most of the Yugoslavian Jacksons were M36, built on the M10A1 hull, and around 50 or so were M36B1 on an M4A3 hull.