Truck losing power slowly while driving

I drove it home from the shop went to class it did not start but that was a loose wire, then I left town for two days ( not in the car in a rental)and this was first time since getting it fixed I tried to drive it, So not even a week, when I took it to the shop one of the problems was it was not starting and I asked them to check the alternator but it is worse now than when I put it in.

Thank you fixitmr for your response