We have measured the effect of in-plane magnetic field on tunneling resonances between transverse X states in GaAs/AlAs double-barrier structures under high hydrostatic pressure. Current-voltage and conductance-voltage measurements performed at pressures just beyond the type-II transition, and at fields up to 15 T, reveal clear field dependences of resonances originating from the Xt(1)→Xt(1) and Xt(1)→Xt(2) tunneling processes. Their behavior is consistent with a Lorenz force analysis, and th...