I am replacing a GFI electrical outlet that went out in the back of our house. It is hooked up on the line to the outlets in our garage. I am using a Sperry Instruments three pronged electrical circuit tester to test the outlets. The GFI that I replaced is now working properly based on the correct lighting on the circuit tester, but the outlets in the garage are giving me a reading that is listed on the tester as hot/ground reverse. However, the outlets in the garage were working properly before I put the new GFI in, and they are still working, but I am getting that reading. Any suggestions?

Could be that they were resversed before and you had no reason to check them. Trust your tester and reverse the wires. If that doesn't fix things get back to us.

Before I went putting a black wire on a green screw and a bare on the brass, I would do some more checking. Better yet, wait until tkrussel answers.

What I would check is to be sure the feed to the GFI is connected to the Line of the GFI,both the black and white, and be sure the downstream outlets you are protecting is connected to the Load side of the GFI. You may have either got these wires mixed up or did not realize there is a Line and Load on the GFI

I would not reverse the black and bare wires. This would mean the bare wire is live, which cannot be.The problem causing this issue needs to be found and corrected so the polarity of each wire is correct.

Best to use a voltage tester with test leads to measure voltage across two wires. Should be 120 volts across the black to white, and black to bare ground, should be zero or close to zero across the white and bare ground.