So the half million mile 4th gen I was driving finally kicked the bucket, lost 3rd and 4th gear

I ended up picking up a nice 01 I30 with right around 117K on the clock and a few problems.

The biggest thing that bothers me right now is the power loss im getting over 3500 RPM.. I'll go WOT and shes got great power up to around 3500 RPM before she falls right on her face.. Hard. So much so that I may only gain 4 mph in the remaining 3K RPM. It doesnt feel like its slipping, but who knows.. The tranny fluid looks great (which could go either way) and I only have one code.. The Cat is bad. Could a cat be whats causing these issues? I immediately though VIAS, but at that low of an RPM something seems amiss..

 

Usually something like that is because of a bad maf.
Very common problem. Revs up to about 3k and it just doesn't go anywhere.
No codes?

Pop the maf out the housing and hit it with maf cleaner see if that
does anything.

 

MAF issues are often more persistent around 2500RPM, and would hold the RPMs below that threshold. I have full range of RPM's, leading me to believe that the MAF isnt the culprit. This problem however is officially intermittent as of 20 minutes ago when I took it for a ride and it didnt occur.