The ion temperature gradient‐driven mode, in three dimensional sheared‐slab geometry, is investigated using fully nonlinear and low noise, weighted‐particle gyrokinetic particle‐in‐cell models. Comparisons between the two models are made and in certain regimes the agreement is good. the adiabatic, Boltzman response model is used for the electron density but alternative treatments are discussed in relation to the development of equilibrium poloidal shear flows. Single and multiple rational surface results from nonlinear simulations are presented for parameters relevant to present experimental regimes. Quasilinear versus turbulent saturation dynamics is contrasted and the ion thermal diffusivity is enhanced by nonlinear interaction between modes with different rational surfaces. Kinetic mixing length diffusivities give good estimates of the radial ion thermal flux measured in the simulations.