Perpendicular magnetic tunneling junctions (pMTJs) as true random number generators (TRNGs) have been investigated by means of high-Temperature micromagnetic simulations using MuMax3. An in-plane applied field, which lowers the energy barrier for thermally activated reversal, can be used to control and increase the bitrates. We study the attempt rate and the energy barrier for 10 and 40nm diameter devices in various applied magnetic fields. At room temperature, the presence of the field leads to orders of magnitude increase in the bitrate, up to ∼ 100MHz.