Polymer solutions in nanoscale slit pores and undergoing uniform pressure gradient (Poiseuille) flow are investigated via generalized dissipative particle dynamics simulations. In particular, the trend of cross-stream migration of the polymer chains during flow is investigated as a function of Schmidt number through varying the strength of the two-body dissipative and random forces in the dissipative particle dynamics formalism. For a given polymer Solution, a migration away from the walls is observed as Schmidt number is increased. For a given Schmidt number, a migration away from the walls is also observed with increasing the driving force for relatively short chains. However, for long chains, a migration toward the walls is observed with increasing the driving force. We also analyzed the effects of channel thickness and temperature oil the trend of the cross-stream migration of the polymer chains.