A GFR of 54 is something to be concerned about, but not worried about if that makes sense. You should probably have a 24 hour urine test done to confirm the results. That is a reliable test.
I had a GFR of 53% about a year and a half ago. I went hard core with the kidney diet for the next six months and it raised to 65, and then I still did the diet but not as stringently and my numbers rose to 74% at my last test about a month ago now. This is unusual, usually the diet will just help you maintain your numbers, but it is still important to follow if you do have chronic kidney disease.
And it also means no ibuprofen, aleve, aspirin, anything that is considered an NSAID. Tylenol is okay. Those are very hard on the kidneys.
Congrats on being clean for a year - that is a big accomplishment.