The potential of QENS (quasi-elastic neutron scattering) to study molecular diffusive motions is well established, but in nematic phases it has not measured up to expectations due to the complexities of such systems. In this work we report the results of a detailed analysis of QENS data obtained for partially deuterated ethoxybenzylidene-bis-butylaniline (d-EBBA) in the aligned nematic and isotropic phases. The spectrometer used was IRIS at R.A.L.; such instrument is unique for this purpose in that it features a reasonably extended q-range together with high resolution. Although some problems still remain, we were able to determine unambiguously rotational (spinning) and translational (perpendicular) diffusion coefficients and their temperature behavior, and analyse some possible rotational diffusion models in the light of the experimentally determined EISF (Elastic Incoherent Structure Factor).