95 Phazer what spring to raise engagement ?

[Vmax540]

I have a 1995 Phazer ST does anyone have a recommendation to what spring would raise engagement from 2800rpm to ~3500rpm ? The clutch is in very good shape and is a YXR and all stock with a new belt, 43.8 weights and a red/blue/red spring and is engageing at ~2800. The center to center, offset and belt deflection are all in specs. Thanks for any help !