I mentioned in the Fuel Discussion forum that I am using RXP in my 99 Cavalier, I'll do a writeup when I get more data on how it's working.
So far, day #2 I have noticed that the cold-running hesitation has come down by about 50%. It used to be when I pull out of my house, and drive to get onto the main street I would get some hesitation when cold when I punched it. That was cut down about 50% this morning.
We'll see what I find over the next week or so. It's a 4 cyl, so I'm not going to see a ton of power come back. If I get 1 MPG more, then it's worth the $6.99 for the 2.5 oz bottle.