Yukon- check engine light and service battery charging system.

Have a Yukon, when I was driving battery light came on along with message "service battery charging system" then all lights/sensors come on such as ABS, airbag, tire pressure, Stabilitrak off, traction off, check engine light, etc.  Once all the lights come on, then the lights begin to dim followed by the truck dying.  I then have to charge for about 30 minutes and can drive about 15 miles before it does it again.   What could possibly be wrong with truck?  I've been told alternator, to needing an new electrical system, to a new battery.  
A month ago, I had the truck checked out because I kept getting the "check engine" light.  The transmission company a took it to said it was a Throttle system error.  When the technician goes to fix the Throttle and replace with a new one, the light went off for about 30 minutes of driving then returned back on.  The technician could not figure out what was wrong and suggested I find a mechanic specializing in electrical system.  I did not get charged for this service.