Q: I need a alternator my Vin is 1GCGK23U44F245647 could you tell me if I need a 105 or 145 amp

Assuming the alternator is original, and thus has never been replaced or substituted with a part that is non-original, you can quickly tell which one you have by reading the tag on the alternator. You will see a tag that is marked "K68" or "KG3". "K68" designates a 105 amp alternator. If the tag reads "KG3", it is a 145 amp alternator. It is recommended that you use the original AC Delco vended alternator. These units are re-built and are very readily available at reasonable cost. I would not bother with other vendors in this particular application. If you desire, YourMechanic will professionally replace the alternator at your location and test the charging system upon completion. The service to request would be alternator replacement.