PROBLEMS. Do they ever stop?

Anyways, I have a 2003 Chevy 5.3 ecsb and I am having some problems, The truck was a special order from the dealership with a bunch of add-on's, It's a Lt so it has onstar, bose, heated/power front seats, dual climate-control digital, steering wheel control's, just about every option you can get from the factory. Well my gauge cluster bit the dust a while back and I haven't had the time or extra money to fix it yet, I was on my way back from my uncle's hunting camp and saw a salvage yard and stopped, an older man owned it and I told him what I was looking for and showed him the gauges, he said I have a few of those trucks back there just go ahead and see if you can find what you are looking for. I pulled 3 that where the same as mine, I stop on my way out and told him I found 3 but didn't know if they where the right ones or would work or not, he said you can have them. I get home and change them out and all of them worked as far as the gauges, my steering wheel controls didn't work, the message part would just say the mileage which I didn't care about I took one apart and used the stepper motors in mine and it worked for a few months and the same thing happened. Well a few days ago I took mine out and put in one of the other ones so I would have gauges, I wasn't worried about the other crap right now. Well the other night I was driving home and my bat. light came on, my volts where at 14 and I have an aftermarket T.V. and it has a setting I can switch to that shows my volts and it was reading around 14 well the gauge started dropping and my T.V. said 11.1 and then it started flickering on and off, when I pulled in the driveway the gauge was around 9 volts. I have a new yellow top optima battery, I unhooked the battery over night and plugged it in the next day and bam the gauge was at 14 volt's and no light, drove the truck up the road and the same thing started happening, got home pulled the alternator, called around to the Chevy dealership, Napa, etc... and no one could tell me what alternator i had in the truck, I got to looking at it in bright light and could see 105 A 12 V stamped on it. I cant see this truck having a 105 AMP alternator in it. I just changed out a neighbor's alternator and we called a auto-parts store and they said there is a sticker in the glove box, alright I have it, he told me what row and where the number would be, I found it and he said its a 105 AMP. Sure enough it was. They didn't know what I was talking about with my truck when I called. Is there a way besides that stamp that I can tell which alternator this is?
Sorry for the rant, I am having more problems with this truck it is driving me crazy.
Thanks for any help.

Also I am going to attach a picture of something on the motor if anybody can tell me what this is I would appreciate it, It has the green cap on it.

 

Try the pictures one more time.

 

What is your reasoning for why it can't be a 105a? That's the common alternator on these trucks?

 

Doesn't mean you can't put a larger alternator on it. Ask for a 145 amp unit.

The line with the green cap is the Evap purge lline.

 

You will most likely have the 105 amp alt unless you have it swapped to the larger 145 amp unit. This can be done but you will need a bit longer belt as the 145 amp case is bigger. I would recommend doing this if you have a lot of extra accessories your trying to power. Look at an 03 Silverado SS for the 145 amp alt.