2001 Ford Taurus Possible Misfires

I got to look at this Ford Taurus V6 when i get into gear i can feel misfires but the pcm wont show any misfires! So I did the cylinder drop test on the coil with the test light . I found something strange the 3 front cylinders are working correctly but the 3 on the rear side appear to be contributing sort of half way . The bank on the rear side is running lean as well and i checked the exhaust back pressure is bouncing from 0-3 psi. I just don't have enough experience to tell if this back pressure reading can make it run lean?? And even make the cylinders work halfway their normal power? Thanks! Sorry almost forgot this , the customer said had replaced plugs , wires and coil pack. I Inspected wires and plugs and everything is in correct order.

3 psi is high for back pressure. What is the pressure at 2500-3000 rpm?

test injector flow yet?

I don't know what you have for a scan tool, but the most reliable way to ID misfiring cylinders, (well, the way I prefer) is using global OBD.
This video shows how to find the information close to the beginning. In this example however, the codes and memory have been cleared, so all the values are at 0.
Which version of the 3.0l V6 does this Taurus have?
On the DOHC 24v Duratec engine, the rear bank is hard to access. Some people will change only the front bank spark plugs. I think someone here referred to that as a "sunnyside tune up".
Any chance your Taurus got the same treatment?

Just for my info, what exactly were your trims for both banks?

Anything's possible, but usually a restricted exhaust will cause a rich condition on the same bank, and a lean condition on the opposite bank. This is caused by differences in volumetric efficiency across banks.

Also curious to know which engine this Taurus has. The Vulcan is OHV, almost no chance of a timing problem, but the Duratec is DOHC...