99 silverado not charging after new alternator and battery

Went and go myself a new alternator to a local parts store, after I told him I had a 2000 silverado truck 5.3L vortex motor and he ask me if I had heated seats and all.He figured that my truck needed the 135 amp alternator (the big one) After I Installed the new alternator the battery light was still on and still not charging.... Brought it back the next day and it was another salesman.... I told him that I just installed new alternator and was not charging..... That then he told me that chev will only take the same amperage as the original one or the (ECM or computer will not allow it to run) and only GM or Chev does that... Gave me a 12v 105A n instead and I changed it right there and it works like a charm.....Therefore you can not go for a more powerful one........