If you have the valve timing correct, I'd think the mechanic is wasting time and effort playing with the cam sprockets.

I "think" the 3.0L injectors are bank fired, but they may be batch fired - I'm not sure. Either way, you'll probably find the problem in either the ECU or the injector wiring harness.

You only have one o2 sensor, so if it's within spec value, it will signal the ECU to open all injectors (whether batch or bank fired) for the same duration. A bad harness could shorten injector pulse time on one bank - since each bank of the injector power connections is joined inside the harness..... 2x 3-into-1, then 2-into-1 before the plug.

Check the connector at the firewall - cycle a few times, spray with electrical contact cleaner (Radio Shack has it).

Another remote possibility is that the injectors on one side are gummed up and sticking - although that might not show up on the scope, since the electrical pulse length is what is being measured - not the actual opening time.

IF - and I'm not certain - the injectors are bank fired, the problem could also be in the ECU or the harness.

If I had to bet, I'd suspect a bad injector rail harness.

Frank