Vertical magnetotransport measurements are used to investigate resonant transport processes in strongly coupled InAs / GaSb superlattices. Sample I-V curves display Stark-Cyclotron resonance and longitudinal-optic (LO) phonon mediated transport features. Resonant tunnelling features change dramatically above the magnetophonon condition suggesting that the Landau levels are renormalized due to interaction between LO phonon's and electrons.