Let A=\left[\begin{array}{ccc}\cos \theta & 0 & - \sin \\\\theta \ 0 & 1 & 0 \ \sin \\\\theta & 0 & \cos \theta]\end{array}. If for some \theta \in(0, \pi), A^2=A^T, then the sum of the diagonal elements of the matrix (A+I)^3+(A-I)^3-6 A is equal to \_\_\_\_ . [4 Apr 2025 Shift 1]

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