the slowness your experienceing has to do with your charging system. your system pulls power, AC,lights, Etc. and thenwhen you try to move windows, they hardly get any juice.
you could upgrade alternators or upgrade the "magic 3" wires
the wires are:
1. alt to batt (+)
2. Batt. to ground chassis
3. Engine to Chassis (ground)
the engine is the best ground in your entire car, but connecting it to the Chassis it provides a link to any metal surface in the car.
batt to chassis is a simple ground point. by connecting to chassis it is also connected to the engine block
alt to batt increases charging capabilities.
use no smaller wire than 4 guage.