Very high intensity and short duration of TGFs make them difficlult targets for spectroscopy due to intrumental effects involved. In this paper we present a Multi-Scale Running Correlation Analysis of TGF light curves recorded in different energy ranges as a spectroscopy tool, alternative to traditional spectral fits. Besides being more rubust to dead time and pile-up effects, this method allows for time resolved spectroscopy with up to an order of magnitude better time resolution. Results for TGF recorded by GBM instrument are presented and discussed.