The series goes like this

4 3 3

5 4 4

3 5 5

4 ? ?

Its a series with groups of three numbers which in turn has two groups with the first digit belonging to one and the 2nd and 3rd together forming another one (Both are equal to each other as you can see above). Both groups are having the numbers 3,4 and 5 running in cycles. So the next natural set should be

4 3 3

and then the next set would be

5 4 4

so the question marks are to be replaced with 3 3 5.