Anders, you mentioned using a balance-bar system presumably with dual masters. Such systems can be used either with or without a vacuum booster. Do you use one? Vacuum boosters can fail their internal check-valves and lose their vacuum-boost capacity.
If pads glaze from hard use or lack of proper break-in, brake stopping power drops radically. Might be you simply need new pads or the old ones roughed up with scotch-brite or fine sandpaper, along with the rotor surfaces. Wilwood calipers usually come with their 'Polymatrix B' pads; I prefer Porterfield sports-racing pads for street Panteras.
PANTERA INTERNATIONAL
A DE TOMASO CAR CLUB
Presents the De Tomaso Forums
The On-Line Meeting Place for De Tomaso Owners and Enthusiasts From Around the World
Clicking on the banner will take you to the sponsor's website.