2007 1500 Silverado AUX feedback and possible short

[Whitney]

so my 2007 silverado is having issues. It has about 89,500 miles on it. The alternator was replaced about a year and a half ago by Murdock Chevrolet because it was acting possessed (Locks locking and unlocking, gauges freaking out, etc.) Every thing was fine until a couple months later. It did it again and was acting like it was going to stall. They did a full system check and found out I had a plug converter in the compartment plugged in and it was being a parasite. ($200 to find this apparently and unplug the damn thing)
And this entire time the AUX would continually give feedback off and on depending if I hit a bump or something. Tried a ground loop cable, that didn't work, tried different cables and they wouldn't work.
Got rearended and when they fixed the bed we had backup sensors installed. (Had mom tell them about the feedback issue and it didn't happen when they looked at it so they just gave us, yet, another cable)
Well now, not only is the Aux putting out feedback again but the sensors for the past month have been acting like there's something behind me on my driver's side each time I put it in reverse.
Last friday the truck started acting possessed AGAIN. Took it to Charlie's and they tested the battery okay and suggested it might be the Alternator and to have Murdock replace it because it is under warranty.
Took it (Limped it) to Murdock, they said the Alternator was fine and doing what it was supposed to but the battery was not holding a charge. They didn't find any draws in the system or anything. So I go to Walmart and get a new battery installed.
AUX is STILL giving feedback. Backup sensor STILL being a bitch.(But not as much).

I am scared to death of driving my beloved truck. I think there is a short somewhere and wires crossing.
SOMEONE PLEASE HELP!
None of the mechanic shops around can help me.
We already put $500 down on new tires and $1000 on fencing. I don't know what to do!
I have to haul my horse to Grand Junction (5 hour drive from here in Utah) in the first of June and don't want anything bad to happen.