Having Dobinson springs can very well mean that your lift is more than 3” unless your rig is quite heavy.Best way to check the angles? I have delta 3” arms and 3” front dobinson springs.
I explained how to get an idea of your castor angle in a prior post. The main thing here is that you don’t spend money on a DC shaft that won’t correct your vibration issues. What you also need to determine is the angles of the companion flanges relative to each other and your actual lift height as measure from the center of the hub up to the fender lip.
Posting a photo of the Front driveline installed from the side would be helpful to us.
Is the pinion nut still tight? Does it feel sloppy when you twist the flange left and right?
