A few more thoughts:

Golf is a game of opposites. To get the ball up, you have to strike it with a downward blow. When you hit your 3 iron off the tee, you may actually be catching it with a slightly downward blow. Try moving the ball back just enough to where you catch it at the bottom of your swing.

Your 3 and 4 iron shafts may be too stiff. I used to have a set of clubs with shafts that were too stiff. I couldn't hit the 3 iron any further than I could hit the 5 iron because I couldn't properly load (flex) the shaft on the downswing. You may want to have a local pro or golf shop check to make sure your shaft stiffness matches your swing speed.