Welcome!
By "struts" do you mean the coil springs?
How have you verified they are the same spring rate as the old ones?
Assuming they are the same, new springs do take awhile to "settle". A lot of people (me included) cut some coil off of new springs before installing; many cut 1 1/2 coils...I chose to cut 3/4 of a coil. It sat great IMO.
Did you tighten the suspension (upper/lower control arms, etc) while vehicle was raised or with the car sitting on it's own weight ( which is the correct way...same principle applies to the rear suspension) ?