Will upgrading gt torsion spring to fx torsion spring help in rear sag

[phazerwill]

I have 10,200 miles and just rebuilt both shocks rebushed and greased rear suspension and have more sag than I feel is acceptable. I think the gt torsion spring is 2100 and the fx torsion spring is 2500. I have installed the high gear bushing at about 5,000 miles and that had helped greatly. Or has anyone experiance high mileage phazers that the torsion springs start to weaken and need replaced? thanks, will