We present an example of an exact quasiperiodic localized stable solution with spatially symmetric large-amplitude oscillations in a nonintegrable Hamiltonian lattice model. The model is a one-dimensional discrete nonlinear Schrödinger equation with alternating on-site energies, modeling, e.g., an array of optical waveguides with alternating widths. The solution bifurcates from a stationary discrete gap soliton, and in a regime of large oscillations its intensity oscillates periodically between having one peak at the central site and two symmetric peaks at the neighboring sites with a dip in the middle. Such solutions, termed "pulsons," are found to exist in continuous families ranging arbitrarily close to both the anticontinuous and continuous limits. Furthermore, it is shown that they may be linearly stable also in a regime of large oscillations.