We had our stand up shower redone a few weeks back but we wanted to wait until we've put it to good use before posting any comments.
Long story short, you need to go with Tile Grout Restoration. The finished product has been nothing short of AMAZING.
The team was able to give me a quote over the phone and it was in the ballpark of others I checked out but liked that they focused on this type of problems and didn't try to be a jack of all trades. They managed to slip me into their schedule which was great even though they were fully booked for weeks. They tore out the crappy old grout, put some bad a$$ stuff in and then resealed it all and re-caulked the whole shower.
On the day of, they showed up on time. Don't let the burly man look fool you, they were the nicest gents I've ever met. Job took them about 5 hours but as said, I don't regret a cent that we spent on it. I have already passed their info onto other in our complex because I'm that confident in their work. I have more work coming up as well and I will definitely be using them again.