I was talking about the Battle of Barrett's Farm in July 1864. Federal forces were commanded by Slocum, not really sure which other generals were with him at the time.
As far as other instances when Grant, Sherman, and McPherson would have convened at Barrett's Farm, I don't think there was ever a point in the war when all three generals would have been in that particular location. May 13th, 1863 McPherson and potentially Grant was near Barrett's Farm but Sherman was on the Raymond Road. May 14th, all three men were in Jackson. May 15th, McPherson moved to Bolton, Sherman and Grant were still in Jackson.
Sherman would have passed through the area and back again in July 1863, but McPherson was acting military commander of Vicksburg and remained in the city IIRC.
Sherman would pass through the area again in February 1864, but Grant had already been summoned east, and McPherson's Corps swung south past Barrett's Farm in an attempt to beat the Confederate defenders blocking the Jackson-Clinton Road into Jackson (again, IIRC).