Charge transport is investigated in high-mobility n-channel organic field-effect transistors (OFETs) based on poly{[N,N'-bis(2-octyldodecyl)-naphthalene1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)} (P(NDI2OD-T2), Polyera ActivInk(TM) N2200) with variable-temperature electrical measurements and charge-modulation spectroscopy. Results indicate an unusually uniform energetic landscape of sites for charge-carrier transport along the channel of the transistor as the main reason for the observed high-electron mobility. Consistent with a lateral field-independent transport at temperatures down to 10 K, the reorganization energy is proposed to play an important role in determining the activation energy for the mobility. Quantum chemical calculations, which show an efficient electronic coupling between adjacent units and a reorganization energy of a few hundred meV, are consistent with these findings.