I have wired a GFCI outlet in my garage. There is power to the outlet, but there is not enough power coming through it to run a fan I was using to test i.t The regular outlets on the circuit work fine. With the GFCI outlet the fan will turn but only barely, there is power coming out but not enough. Any suggestions would be appreciated.

The voltage in correctly wired AC circuits in dwellings are not variable without special controls...
So, the GFI is not connected... or it's tripped.
Re-check your wiring and use a voltage tester to zero in
on the problem.