Welcome to the forum
I assume the power from this engine was OK prior to timing belt change, right?
What were the compression numbers?
2.3l should be in the 170psi range
Cam sensor will effect MPG not power.
And you test for exhaust blockage with Vacuum gauge while engine is running, not sure how you could test it by removing an exhaust pipe?????
You also test engine condition in general with a vacuum gauge, this $25 tool can help you alot.
Mechanic should know this???
Crank sensor will effect power, it runs the spark timing.
Crank sensor is working or engine wouldn't start, but it reads a tone wheel that was removed when timing belt was changed, and it is a VERY precise timing.
A little slop in the tone wheel means spark is happening too early or too late, which lowers power.
This is a long shot since it should be obvious if tone wheel was loose, but have read of it happening.
Check spark timing with timing light, not OBD2 reader
This is a picture of 2.3l harmonic balancer with tone wheel on the back: http://www.ebay.com/itm/Engine-Harmo...FWe7yw&vxp=mtr
It looks like a gear, but has 1 missing tooth, at 1:00 in picture
The missing tooth tells computer when #1 cylinder is at top dead center, so that sets up the spark timing for all 4 cylinders, it can come loose from the balancer, so shifts slightly one way or the other.