There's this test http://www.englishpage.com/verbpage/verbs12.htm
The relevant part is:
I have visited so many beautiful places since I (come) to Utah.
Apparently it's more natural to say verb in a Past Simple after "since":
"since i came" = 40,900,000 results
"since i've come" = 8,830,000 results
But is this grammatically incorrect to make it Present Perfect?
The rule says:
We use the Present Perfect to say that an action happened at an unspecified time before now. The exact time is not important. You CANNOT use the Present Perfect with specific time expressions such as: yesterday, one year ago, last week, when I was a child, when I lived in Japan, at that moment, that day, one day, etc. We CAN use the Present Perfect with unspecific expressions such as: ever, never, once, many times, several times, before, so far, already, yet, etc.
Does the word "since" make a time specific?