the torsion can be adjusted setting it in another hole for more torsion. My Charger ( no spoiler ) got two springs, one attached on each side. Maybe due the bigger lid ?

A friend of mine molded the trunk lid on his 71 Charger like making somehow a ramp to work like a spoiler with bondo, and never took care of the added weight... allways had to use something to keep the trunk lid open untill I told him to increase the torsion giving one extra hole on each side... problem solved