[en] The anomalously large thermal transport observed in tokamak experiments is the outstanding physics-based obstacle in the path to a commercially viable fusion reactor. Although decades of experimental and theoretical work indicate that anomalous transport and collective instabilities in the gyrokinetic regime axe linked, no widely accepted description of this transport yet exists. Here, detailed comparisons of first-principles gyrofluid and gyrokinetic simulations of tokamak microinstabilities with experimental data are presented. With no adjustable parameters, more than 50 TFTR L-mode discharges have been simulated with encouraging success. Given the local plasma parameters and the temperatures at r/a≅0.8, the simulations typically predict T_i(r) and T_e(r) within ±25% throughout the core and confinement zones. In these zones, the predicted thermal diffusivity increases with minor radius robustly. For parameters typical of r/a > 0.8, toroidal stability studies confirm the importance of impurity density gradients as a source of free energy potentially strong enough to explain the large edge thermal diffusivity, as first emphasized by Coppi, et al. Advanced confinement discharges have also been simulated. The dramatic increase of T_i(0) observed in Supershots is recovered by our model for dozens of simulated experiments. Finally, simulations of VH and PEP mode-like plasmas show that velocity-shear stabilization of toroidal microinstabilities is quantitatively significant for realistic experimental parameters