Trinucleon longitudinal response functions R L (q, ω) are calculated for q values up to 500 MeV/c. These are the first calculations beyond the threshold region in which both three-nucleon (3N) and Coulomb forces are fully included. We employ two realistic NN potentials (configuration space BonnA, AV18) and two 3N potentials (UrbanaIX, Tucson-Melborne). Complete final state interactions are taken into account via the Lorentz integral transform technique. We study relativistic corrections arising from first order corrections to the nuclear charge operator. In addition the reference frame dependence due to our non-relativistic framework is investigated. For q ≤ 350MeV/c we find a 3N force effect between 5 and 15 %, while the dependence on other theoretical ingredients is small. At q ≥ 400 MeV/c relativistic corrections to the charge operator and effects of frame dependence, especially for large ω, become more important . In comparison with experimental data there is generally a rather good agreement. Exceptions are the responses at excitation energies close to threshold, where there exists a large discrepancy with experiment at higher q.