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GMC Wont Start Unless Get A Jump

Answers
if that's what is happening, it's not your alternator. Most likely culprits are either a) the battery, or b) a parasitic drain on the battery that sucks out its charge that accumulated during the day.
So you have to have the battery "loaded tested" (which can only be done on a battery that has been properly charged in the first place) and if that checks out okay, then you have to diagnose for a "parasitic drain", which can be tested in the manner described below:
Testing for Parasitic Drain