If you suspect the cat do what @chucktobias recommends to easily rule that out.

Other forum guys can correct me if I'm wrong but 4,000 rpms sure doesn't sound like Limp Mode. That's usually under 3,000 rpms.

So if you've ruled out a cat obstruction that would leave stuff like valve timing but I don't think the 2000 CRV had VTEC (you can look to see).

So now you're thinking about stuff in the powertrain/fuel delivery management.

Like MAP sensor, TPS sensor, O2 sensor, ... all that stuff. Hook up a scanner and graph it.

Don't overlook that this could be caused by a bad alternator/charging wiring issue.

A bad diode in the alternator may still charge a battery but under load it  will  affect several sensors and the PCM isn't going to like that.

So for example, if you hook up a scope to the alternator and do a ripple test, the top capture is what you want to see.

The bottom capture is a bad alternator.

This is just a guess. Given the age and the make and model, and the fact you are getting no codes, it is likely the catalytic converter. I believe Scotty has a video (And I ran into a few others over the years) on how to test the catalytic converter. Make sure to verify before swapping out parts. Cats are expensive. 

Posted by: @scottydaman2023

Can't I just unbolt the cat bang it out and rebolt

No. However, you could try removing it and cleaning it using soap and water.

https://www.edmunds.com/car-maintenance/how-to-clean-a-catalytic-converter.html

Before doing anything else though you should use a gauge to check for excessive back pressure. That will tell you if the converter is clogged.

Well limp mode is a generic thing. But it should always have some kind of code. If it has no code odds are the computer has gone bad or somehow wiring or A sensor has gone really bad and that stopped information from being relayed from the computer. In that case you go around on plugging all the sensors one at a time and then when all the sudden you start getting data you know that sensor's bad.