Observations of gamma-ray bursts up to z similar to 9 are best suited to study the possible evolution of the universe equation of state at intermediate redshifts. We apply the Combo relation to a sample of 174 gamma-ray bursts to investigate possible evidence of evolving dark energy parameter w(z). We first build a gamma-ray burst Hubble's diagram and then we estimate the set (omega(m), omega(?)) in the framework of flat and non-flat ?CDM paradigm. We then get bounds over the wCDM model, where w is thought to evolve with redshift, adopting two priors over the Hubble constant in tension at 4.4 sigma, i.e., H-0 = (67.4 0.5) km s(-1) Mpc(-1) and H-0 = (74.03 1.42) km s(-1) Mpc(-1). We show our new sample provides tighter constraints on omega(m) since at z = 1.2 the case w <-1 cannot be fully excluded, indicating that dark energy's influence is not negligible at larger z. We confirm the Combo relation as a powerful tool to investigate cosmological evolution of dark energy. Future space missions will significantly enrich the gamma-ray burst database even at smaller redshifts, improving de facto the results discussed in this paper.