Yes, if you don't have one, the LS ecu is a must. That's almost certainly why the car isn't running so well. I believe redline is about 7k.

A/F guages (the kind with the little lights) are pretty much useless, so I wouldn't worry too much about what it says.

If your speedo is off, it's probably because of tire/wheel size. A swap shouldn't change your speedo reading.