The dynamics of the fluid flow within faults plays a critical role in the evolution of fault strength through the seismic cycle. The key processes that control how fluids affect fault slip behavior are the evolution of fault porosity and fluid recharge during slip that, in turn, determine dilational strengthening or compaction weakening. Despite the significance of these processes, high-fidelity lab measurements that include the evolution of porosity, fluid pressure and frictional properties are sparse. Here, we report such data for drained and undrained velocity-stepping experiments from 3 to 300 µm/s on natural fault gouges from the seismogenic zone of injection well 16A (2050 - 2070m) of the Utah FORGE EGS site. We conducted a suite of experiments under fixed normal stresses (44 MPa) and pore fluid pressures (13, 20, 27 MPa) corresponding to pore fluid factors between 0.3 and 0.65. We carefully monitor the volumetric strain and show that the dilatancy coefficient of the material ranged from 5 to 12 x 10-4, and showed minor sensitivity to fluid boundary conditions. In some cases, we see that larger slip velocities cause a transition from dilatancy strengthening to compaction weakening via fluid pressurization. Fluid pressure diffusion across the fault evolves during shear suggesting that permeability asymmetry, up to 4 orders-of-magnitude, is required to explain the interaction between fault stress, dilation and fluid diffusion. We posit that the spatial-temporal pattern of pore connectivity creates a spectrum of fault drainage conditions, ultimately controlling the mode of fault slip.