Gurfateh

As per Nihungs they say that,they consider Dasham Granth and Sarbloh Granth both as Guru also.
Reference:: Sikh Philosophy Network http://www.sikhphilosophy.net/sikh-sikhi-sikhism/666-guru-granth-sahib-history-arrangements-text.html

but Dasham Granth was made long time after Guru went to Sachkhand and is infact a compilation of more then one book,they could be at least three which Bhai Mani Singh Ji compiled with Mata Sunder Kaur Ji's consultatoins.

So as that Granth did not exist at the time of Guru so it can NOT be Guru.

Then yet there was another Granth called Sarbloh Granth kept in Hajur Sahib and perhaps competed there only and reached Punjab later.
Reference:: Sikh Philosophy Network http://www.sikhphilosophy.net/showthread.php?t=666

It could be from Guru but it clearly states that Guru has Tweleve Form is Ten Gurus,Guru Panth and Guru Granth.

So this Granth gives testomany to Guru Granth Sahib being Guru by Tenth Master himself.

But das can say one more thing that since the First Master Sabad Guru was held as Satiguru(Guru of First Master).

And in Sau Sakhi ,Charan Pahil or Pahul before Baptism of sabre was done by dipping cloath of the corner of Guru Granth Sahib Ji in water and thatb water was given to baptised.

So it is possbile that Guru Granth Sahib Ji are our Guru even before symbolic handing over the Guruship to them at Hajur Sahib.

Forgive das if mistake is done.