did you re-adjust the pinion angle? Are the shocks at the correct lenghs & angles to work properly? Do you have a panhard bar from the factory? Has it been re-set for angle?
All of these things become a big factor in the chassis performance not only in braking, but in acceleration too. 5/7 is a lot of drop.
I'm not saying that you didn't do it right- just a few points to check. If you have all of these correct I would start looking for a pinched brake line.
If no pinch & everything else is correct than I would install an adjustable porportioning valve.
But I'm a painter so that's just my opinion..
Good Luck