New bounds are proven on the mean vertical convective heat transport, $\overline{\langle wT \rangle}$, for uniform internally heated (IH) convection in limit of infinite Prandtl number. For fluid a horizontally-periodic layer between isothermal boundaries, we show that \rangle} \leq \frac12 - c R^{-2}$, where $R$ is nondimensional `flux' Rayleigh number quantifying strength internal heating and...