Is Muhammad really the last prophet?

Yes he was. Muhammad (SAW) is the final prophet and messenger of Allah (SWT). Allah (SWT) has stated in the Qur'an that He (SWT) is protecting the Qur'an from mankind's folly and challenges Kaffur to produce a Sura like a Sura in the Qur'an and bring forth their witnesses if they are truthful. Nobody in 1431 years has EVER been able to produce a sura like the suras in the Qur'an and nobody ever will.