Viscoelastic (VE) behavior at elevated temperatures of ultra-high molecular weight polyethylene (UHMWPE) was studied in strain controlled tensile tests, finding that a thermo-rheologically simple linear VE model with temperature affecting only the shift factor gives sufficient accuracy. Indeed, master curve construction after the tests at different temperatures proved that only horizontal shift in log t axis was required. The Prony coefficients of the Master curve found at reference temperature and the dependence of the shift factor on temperature were input parameters in validation simulations of a complex loading ramp where the temperature and the applied strain were changing simultaneously, showing good agreement with the test results. The thermo-rheological simplicity of the UHMWPE implies no aging of the amorphous phase and not changing degree of crystallinity during long term tests, phenomena that were inspected in repeated tests and using Differential Scanning Calorimetry.