Is the Hadith "Whoever recites the last five verses of Surat al-Kahf, Allah will resurrect him whenever He wills at night" authentic?

What you asked about is a weak Hadith. In Sunan al-Tirmidhi, it is narrated from Zirr ibn Hubaysh, who said: "Whoever recites the end of Surat al-Kahf at an hour when he intends to rise during the night, he will rise." 'Ubaydah said: "We tested it and found it to be so." Its chain of transmission is weak due to the weakness of Muhammad ibn Kathir, who is al-Massisi, and it is also mawquf (stopped) at Zirr. What is understood from this Hadith is that if one recites the five mentioned verses before sleeping with the intention of waking up during the night, Allah Almighty will grant him success in that. However, the Hadith is weak.