Diagnosis
Yes. The counterbalance spring is incorrectly tensioned. The Classic III uses an adjustable spring to offset the dome's weight. It is likely on the tightest setting from the factory.
How to Fix It
Locate the spring adjustment mechanism on the hinge arm. You will see a series of holes (typically 5) on the bracket. The spring pin is currently in one of them. With the dome closed and the aid of a second person for safety, use a punch to drive the spring pin out. Move it to a hole closer to the hinge pivot point. Test the dome weight. Repeat until the dome stays open at 45 degrees without slamming or lifting.
If That Didn't Work
The spring itself may be defective or the hinge bolts are overtightened, creating friction. Loosen the four main hinge bolts a quarter turn. Open and close the dome several times to seat the parts, then re-tighten the bolts snugly, not with maximum force.
Heads Up
Always adjust the spring with the grill cold and the dome closed. Adjusting while hot or with the dome open is dangerous and can lead to sudden failure of the mechanism.