Magnetic-relaxation parameters of the paramagnetic centers-in poly(tetrathiafulvalene) samples with different doping levels were studied by 2-mm-band EPR spectrometry. Electron relaxation time and the rates of intra- and interchain spin diffusion rates were separately determined by the steady-state saturation technique. Anisotropic superslow librations of polymer chains were measured by the saturation transfer technique. The intensity and the activation energy of these librations were found to depend on the sample doping level. The initial polymer features isoenergetic charge transfer by small polarons in agreement with the Kivelson theory. The interchain mobility of the molecular-lattice polarons in doped samples is correlated with the libration motions and is described with good precision within the framework of the variable-range hopping charge transfer mechanism