2005 Durango 4.7L 81,000 miles

Hello all, I have some questions that I need help with. Here they go.

    I have a 2005 Durango SLT with 81,000 miles, and also have a stereo system that includes an amp, subwoofer, aftermarket radio and capacitor.

    1. Lately I have noticed that the A/c in the truck does not get cold while at a standstill like it used regardless of the heat outside. It does get cold once the truck begins to move again. What could be the cause and solution?

    2.  Wtih the A/C it is understood that the truck surges when the compressor engages and disengages, but i also notice that the lights inner and outer dim low and regain normal brightness and the radio (aftermarket) sometimes shuts on and off when the compressor surges. What can cause this and can i replace the factory installed alternator to a 160amp alternator to compesate for the power loss from the sound system?

   3.  Also could changing the serpentine belt be the issue? I know the belt squeals alot when it gets wet (More than normal) and also when the engine starts when cold.

Any help is appreciated, Thanks.