Crusing Power Down

I don't know what to title this thread, anyway when I am crusing in the Camaro to stay at 40 mph in 4th gear I have to be at about 18-19 hundrend rpms. To stay at 45mph in 4th its 22-23 hundred rpms. I know it wasn't like this when I got the car and the only thing I have done is high flow cat. What are some things to check, sparkplugs and wires have already been replaced. This has been happening for about a month so its not bad gas.

Does the car run noticably different at any other times? Idle, acceleration? If it was an automatic I would say check to make sure it's shifting into OD but you have a 5 speed so that's not it. Otherwise I'm really not sure what's going on, give us more details if you notice anything.

Its only when I am crusing, Idle, acceleration etc are all the same as before. I don't think I can really give you more details becasue as far as I know nothing else is wrong. Its still got power when you step on it, its just it takes higher rpms to keep it crusing.

Your tach is off, that's all.