Try a flow test before and behind the converter, to see that its not stopping up.

You'll have to bring it to an experienced exhaust shop for this. Its fairly cheap to rule out exhaust issue as power problem.

K

__________________
1989 420SEL 105575 miles
Pearl Black/Grey

1990 Chevrolet E-Cab C-1500
293,000 miles

1989 Olds Toranado Trofeo'
132,000 miles