srusa
It's hard to pinpoint exactly what is referred to as the "True Gāyatrī" since there are many variations. Guruji in the book "Gifts from the Goddess" did mention a four-legged Gāyatrī with "parorajase savadom" as the final part, and also discussed the Ajapā Gāyatrī, which is a deeper, internalized form of the Gāyatrī Mantra.
However, his teachings primarily revolved around the Śrīvidyā or Tantric version of Gāyatrī which is the Pañcadaśī mantra, and he didn't go into the specifics of chanting Gāyatrī. If you are interested in this topic, connecting with a Vedic guru would be advisable.