granada mk 3 autobox

can anyone tell on a autobox when should 4th gear engage (25-30 as it used to) or 45mph as it does now since an auto spec put in a new speed senser and said 4th is overdrive at 45mph.so am driving around town in 3rd. as its my first autobox am confused am used to a manual box 4th @30mph not 45mph. any help please

45 mph is the correct speed to change from 3rd to 4th.

Brian.