My opinion on removing cats is unless you have some sort of major power adder (ie supercharged, n2o, etc.) just leave them alone. When removing your cats you gain upper end horsepower but as a trade-off lose low end torque. Even with a supercharger when I removed the cats on my truck I noticed a lose in low end torque. Before removing the cats I had to run colder plugs gapped at .035" to keep from having the occasional spark knock problem. Now after removing the cats the exhaust flows better so I changed back to the stock heat range plug gapped .060" & it picked up a little low end power. As of yet it hasn't had any spark knock problems and the truck runs strong .

 

It sounds like there is to little back pressure. Try the next size down X-pipe if your concerned about it. That should bottle neck it up a little for ya. If you can't find one a little smaller, get a cheap one. They don't flow as well as the better ones on the market.