Dear friend,
Sikhs believe in one God only. They lovingly address it by 'waheguru'. The
'trinity' as per
Sikhism is Almighty Himself.
Yes, we find in Granth sahib that Gurus have addressed God as Ram as well. Kindly refer Jap Ji sahib and you will find many names used for Guru i.e God. The following should clarify the concept of God in
Sikhism.
Thaapia na jaae keetaa na hoe|| God exists unaffected by this world beyond all care.[Other meaning that is also assigned is: One cannot establish the God] Aapae aap nir(n)jan soe|| He is beyond creation self existent.
[This concept is called as Saibhung.]
There is following line that you may read in the light of above.I am not giving any meaning to it.
Gur eesar gur gorakh barmaa gur paarbatee maaee||
Hope it helps.
Best Of Luck.