The linear stability analysis of the ITG modes in a plasma slab with an equilibrium ion flow has been carried out by solving the relevant eigenvalue equation for the complex electrostatic fluctuation amplitude , by retaining the electric, the diamagnetic and the gravitational-like drifts. For sufficiently broad Ti profiles, a novel regime with two-branch distributions of unstable eigenvalues has been found, which seems to be characterized by a broad radial correlation length. The plasma density profile and a macroscopic ion flow aligned to the magnetic field govern the relative importance of the two unstable sets of eigenfunctions.