With that much negative caster from only a 2.5" lift Irishjig (and I'm assuming it's caster from your description), either at least some of the C-bushings are in wrong, or your truck had some nasty caster readings already.
Those bushings and a 2.5" lift should have left you with roughly 1-2 degrees positive. Fully four or five degrees from where you are now.
It's not impossible of course. Just more off than normal.
Did you take these readings yourself, or was that from a pro alignment rack?
Adding drop brackets for their additional 4 degrees of offset is not usually a good combination with 7° C-bushings. Too much pinion angle change and potential for the u-joint to bind up.
But every truck is different of course, so with some testing you could determine if yours can tolerate the extra 4 degrees of tilt.
I'd have to say that most EB's could not handle that much, but it can't hurt to check.
Then again, even after all that, you'd only be at 1 degree positive caster. Not enough for a happy driving experience for most EB's. Mine was not horrible at that level, but most who have that don't like how their rigs drive.
So, if you are truly at 3 degrees negative with 7 degree bushings, the ONLY true fix as far as I'm concerned is to cut and turn the steering yokes.
Those are the ends of the axle tubes where the ball-joints attach the steering knuckle to the axle assembly. Commonly referred to as the "inner-C" these days, they are the only component that can be changed to get both good caster numbers and a good pinion angle.
If you end up doing that you would normally go back down to a 2 degree C-bushing and then turn the yokes to get caster.
If you're not sure about any of that stuff, it's been done a lot here over the years, and if you can post up some pics of your situation as it is now, maybe someone can see something and come up with a better solution.
Good luck!
Paul