I'm not running a VSS. I'm not sure what you mean by "runs better". Mine runs like a top without a lick of hesitation, ever. It might run a little more efficiently with a VSS for better mileage (?).
Regarding the flex plate, I'm not sure about GenIII stuff, but if you're running a 5.3 or 6.0, you'll need a dished flexplate and pilot cup for the torque converter snout (Advance Adapters part #712500A). You can probably get the same kit from other vendors. I just bought from AA. On my 5.3 from a 2006 truck, there was a plug in the back of the crankshaft that looked like a freeze plug. I had to remove it with a homemade slide hammer setup that I made with a large bolt. This allowed the cup to sit in the back of the crank like it should without pushing the torque converter away from the crank. Remember, the spacer people talk about is NOT a spacer. It should not push the converter any farther away from the crank. It's just there to keep the torque converter pilot centered.
One other tip about removing the plug from the rear of the crank: I've read on forums that you should NOT use the trick of driving grease into the space behind plug in order to force it out, because crank damage may occur. I found that a large, long bolt (like a 3/4" or something) will thread tightly into the inner diameter of the plug, and you can slide a plate over the bolt before threading it in and hammer it all out. It's been a year since I did it, but that's how I remember it.
