I replaced the OEM muffler with the Walker BTM today and am happy with the result.
First off the truck does not get noisier as I expected.
Before the BTM installation, it goes 60 miles/hour at 2,000 to 2.100 rpm.
After BTM installation, it goes 60 miles/hour at only 1,800 rpm.
In couple of weeks I'd be able to tell if there is any improvement in mpg. For now I feel like it has a tad more power and seems to accelerate a little faster.
It costs $80 for the BTM and $100 for installation labor. I had it welded in instead of using clamps.