Installed Dynomax VT on my 5.0 today
 

Took the factory resonator and muffler off. That was 38 lbs. removed from the vehicle. Had a Dynomax VT part # 17957 installed in place of all that stuff. I'm REALLY happy with it so far. I'll do an update in about six months when it's worn in good.

I am curious as to how much back pressure the Dynomax VT gives when the valve is closed and how much performance gains there are. I have the MBRP 3'' cat back system with their resonator. It is quite loud (straight thru design), but the performance gains are quite noticeable. Even with stock tuning, it gives the impression of having a tuner installed.

I saw a video where they tested a Nissan sports car with full racing exhaust, then they put a Dynomax VT on the car and it made 4 more horsepower at low RPMs. That was a surprise to them. It's not a Ford truck...but it did show that the muffler did well.

I did a lot of reading on many of the different muffler brands/designs. Straight thru designs give the best performance gains. Anything that reduces noise tends to reduces performance, also. There is an optional muffler from MBRP that reduces noise, but at the expense of performance. Since I was more concerned with low-mid rpm performance (towing), I am staying with the straight thru design and quickly getting accustomed to increased noise level in the cab. BTW, my system actually quiets down some at higher rpm (interstate cruising).