The sixth moment of a degree two $L$-function of arbitrary level

Let $f$ be a primitive holomorphic cusp form of arbitrary weight, level and nebentypus. We prove $\int_0^T|L(1/2+it,f)|^6\,dt\ll_{f,ε}T^{2+ε}$, extending Jutila's level-one theorem. The new ingredient is a large sieve comparing the stationary phases in the Booker-Milinovich-Ng transformation at diff