Camshafts. 4 Camshafts, DOHC for each bank. With each having separate cam phasers for the VVT. I know Inertia Motorsports made cams for the 3.5L, but apparently nothing for the 3.6L. Prodigy makes Pistons and Rods and does full engines. I don't think anyone makes cams. A Guy
No cams, the 3.6 is already a wheezing dog down low, cams normally shift torque higher up the rpm range, so new cams would make things worse for the 3.6 under 4000 rpm, smaller cams would shift things down but then you loose the hp on the top end. So I would imagine the 3.6 has the best cams it can have naturally aspirated.
If you want to e.t. quicker, then gearing, stall, suspension mods would cut down your 0-60 mph time, I got down to 5.08 0-60 naturally aspirated and still had room to cut it even more before I supercharged. I got to 4.0 0-60 mph times with the blower.