amp, front speaker, volume problems

I really am stumped with this problem and would really appreciate some insight!

Here's the deal:
My setup worked great for the first month or so, I used test-tones to properly set-up the gain on the amp which was powering my front 2 speakers. Then all of the sudden, I had to turn the volume down a lot to keep the music/speakers from constantly cutting in and out continuously. Now what I've found is that wherever I set the gain on my amp, I can only turn up the volume to a certain dB limit, which is very quiet compared to what it used to be able to do; otherwise, the sound cuts in and out. If I turn the gain down, I can turn the volume up more, but the net effect is the same on the total dB output and if it is exceeded by either gain or volume on the headunit, sound cuts in and out. This all happens using accessory with engine shut off and at idle with car running.

My setup:
-2 Alpine Type R component speakers with the crossovers up front (only speakers in car).
-Alpine 2 channel Amp MRP(ish)-220 if I remember correctly and it puts out either 40 or 50RMS watts to each channel, while the Type R's handle either 90 or 100RMS watts.
-Alpine headunit
-Optima red-top battery when sitting is at 12.0-12.6V, at idle: 14.8-15.0V

Wiring:
-Upgraded big 3 using 4 gauge wire, 8 gauge wire to amp/ground, 16 gauge wire to speakers, ground is excellent on the amp, wires are all soldered making good connections and not shorting anywhere.

All I can think of is that the amp may have gone bad somehow or that I need one that puts out more power; however, it used to sound great at a much higher volume and never cut in-and-out like this. Also the headunit alone was able to run at a higher volume without distortion then it does now currently powered by the amp. Any suggestions?

Try balancing to the left, see if it still cuts out.  If so balance to right and check again.  If it cuts out on one channel but not the other, you have either a bad speaker, crossover or a grounded speaker wire.  If it cuts out with either of the channels driven one at a time, I would look at the powr connections of the amp.  With the system turned up so it is cutting out, connect a volt meter to the power input connections at the amp.   Let us know what kind of voltage reading you come up with.

I will have to test the balance on the speakers and voltage reading on the amp when I get home in 2 weeks; however, if one of the speakers or crossovers were somehow bad, wouldn't the speaker/system sound bad or not work at all volumes? Mine only cuts out through gain/HU-volume combinations that exceed a certain dB limit, but at lower volumes works with no problems...

I am almost 100% all the wires/grounds are fine. This all leads me to believe that somehow the amp has gone bad - is the symptoms I have experienced any kind of indication of a bad amp?

Yes it could be a bad amp.  The balancing of the system is all a part of the necessary troubleshooting to figure this out.  Post your results when you get back.