It is very likely that all these codes are related. I do not think PCM (ECU) had failed. In fact it is reporting what it sees as malfunctions, therefore it work perfectly well. The mix of codes - bank 1 lean, bank 2 rich is puzzling. This means two banks are affected differently. I think you might be on to something with the wrong timing belt installation. Since it is a V6 engine - you have two banks and two camshafts. it is possible that the timing is off on one or on both of camshaft sprockets. As far as timing belt stretching or a problem with a tensioner. What is most likely is the TB is off by one tooth from proper timing. I'd start by checking that first. Who did the timing belt job for you? On one hand you can go back and demand that a shop re-did the work. On the other hand if they are so bad as to miss it first time, where is the guarantee they will not miss it again.

Computer can't tell the timing is off - it "sees" signal for camshaft and crankshaft position and proceeds with ignition and all the other controls. When things do not work, PCM reports - something is wrong...

 

The mix of codes does seem to point to timing being the first place to look. The two lean/rich codes, and the two sensor codes (camshaft and crankshaft position sensors) seem directly related to a timing issue. I would think failure of both position sensors at the same time highly improbable, although I guess anything could happen. (I miss the days gone by when the only thing emissions-wise was the PCV valve). When I find out the demonstrable cause I'll post it. Might help someone along the line.