The 2 biggest restrictions in the system are the muffler and tailpipe. Every bend is is a measurable reduction and the tailpipe has 5 or 6.

I don't know what was OEM on yours but my 99 had a resonator then a muffler and tailpipe.

The muffler and tailpipe rusted out and the bucks down solution was a long 3" 90 deg elbow exiting in front of the rear tire. About $30 plus install.

If I just had to have a 5" overkill system, I could probably piece the majority of it together from a Donaldson truck exhaust catalog. A 5" muffler for W900 Kenworth is $60-$80 and quiet.

Kevin.