The shear relaxation modulus, G(t,gamma), of entangled polymers decreases with increasing magnitude of shear, gamma. A damping function defined as h(t,gamma) = G(t,gamma)/G(t,0) decreases with time and approaches a finite value, h(gamma), at long times. In the tube model theory, the relaxation of G(t,0) is attributed to the reptation process and that of h(t,gamma) is attributed to the retraction along the tube of a chain extended according to the large deformation of the material. We examine, in view of experimental results, an expression h(t,gamma)/h(gamma) = [1 + A(t,gamma)](2) derived from a theory of Doi. Here, 1 + A(t,gamma) is an average elongation ratio of a chain contour in the tube. At gamma less than about 7, the function A(t,gamma) was factorizable into functions of t and gamma, respectively : the reptation process and the retraction process are not coupled in this case. At higher strains, A(t,gamma) is not factorizable and is dominated by modes of shorter relaxation times. Possibly the limited extensibility of chain portions of the order of the entanglement spacing changes the nature of the tube at large deformations. For branched polymers, the fast relaxation modes become dominant even at gamma = 5. This may be in accord with the well-established theory for branched polymers that stress relaxation at vanishing gamma requires the retraction of the chain end along the contour of the chain. This process is essentially the same as the retraction process at large strain, and these two relaxation processes cannot occur independently of each other.