If a truck is faster with a larger ( more fuel limiting) plate, the AFC is not dialed in. Fuel plates accomplish the same thing your foot does. Lift your foot and you do the same thing! If your after milage tune your AFC and put the most restrictive fuel plate avalible.
It seems that most high milage trucks suffer from a weak AFC spring. When you tighten the star wheel enough to get it to stop smoking you are not getting enough travel to reach full fuel. When you loosen it up enough to get full fuel, it gets hot and smokey because the AFC spring is compressing prematurely.
To fix this, stretch your stock spring or replace it with one that when set with a gauge off the truck, puts the star wheel in the middle or a less on the preload adjustment. Make sure you are getting full travel.
Fuel plates allow people who don't want to burn up their engines to mash the peddle to the floor with out having the incovieniance of having to watch a gauge. When a plate is being used to create a fueling curve the AFC is not tuned. The AFC tuning will make or break any set up.
That said, fuel plates have their place - on trucks that are driven by uncaring employees, trucks not running gauges, or that might be lent to your teenager.