Ok, I kept researching online. Here’s the ending story with the resolution.
Replaced the plug on 3 just in case. We let the engine run, pulled the 3rd spark plug, no change in engine sound. Pulled out 2nd spark plug, definite change in engine sound. Decided to do new wires just to be on the safe side. (I don’t think I did new wires last year just the distributor?) Checked the engine while running early Saturday (garage was still dark) sprayed engine with ether, no odd sparks so more than likely no vacuum leaks. Forgot: we reinspected all spark plugs when we did the wires. All looked good and #3 was new so that theory was out. Also, forgot, we added a can of Seafoam Motor Treatment last week, no real change. Also, sprayed the MAF sensor well with clenaer, no change. The codes were still showing for the knock sensor (P0325) and the 3rd bank misfire (P0303). Tried driving it Saturday, ran really really bad. Pedal to the floor and was barely going 40, sputtering. Back to the drawing board. Purchased a 3M Do-It-Yourself Fuel System Tune-Up Kit. The first can, Intake System Cleaner, restores power and performance by cleaning the intake manifold, combustion chamber, and valves. Then we finished off the other 2 cans. Throttle plate and carb cleaner, then the Complete Fuel System Cleaner. Checked van again, slight improvement (25%). Stopped for the day on Saturday. Sunday morning; we pinched off the return fuel line to put pressure into the engine (we were both still thinking a clogged fuel injector). Let it run with the line pinched for about 7-8 minutes then we shut it off. Started it up, instantly noticed a difference. Took it onto I-75 and really ran it and at that moment, it cleared up. It was instantaneous! I reran the codes on my Torque app while we were on the interstate and all of the codes were gone! It purrs like a kitten now. As a matter of fact, it hasn’t ran this smooth in 3-4 years. I will continue to use Shell V-Power gas in it as I always have. I think the combination of the 3M kit and pinching off the gas line did it.
Fuel injectors was what we figured also. Local Nissan dealership quoted us $175 per injector and over $500 in labor. I’m glad we were persistent and figured this out ourselves. Yikes!
Thank you for your response.