Ok, quick update - I had my 4.0+ VT muffler installed with a custom y-pipe. I kept stock over the rear axle pipe with OEM resonator. The muffler works as advertized - sound is just like stock at idle, just a little deeper and a tad loouder with a little growl under 2K RPM. Over 2K RPM it really comes to life and you can really hear it, even at marginal throttle input as the gases flowing open up the valve inside the muffler. Much louder at WOT and the sound is very pronounced past 70MPH., but anywhere up until 70 MPH is relatively quiet. No drone issues, unless you're going 80 MPH, then you just hear the muffler hum, but its not to the point where it is annoying. Overall not bad at all, but I think I would like it a little bit quieter around 2-2.5K RPM. I will give it a try for a little while and will start looking into a V8 LE muffler as my next option. V8 muffler looks like it will bolt right up and since its 2-in/1-out configuration, there should be no problems with restricting the flow, especially from 4.0 engine.
Here are some pics from the install. Both cats dump into custom y-pipe:
Dynomax VT is 4 inches shorter that stock muffler and is placed towards the back of the truck:
Muffer goes into stock tailpipe that retains stock resonator: