If you are on IOS or Android I like justinGuitar's TimeTrainer Metronome app. It has a lot of really nice features. One of my favorite things is I can set it to start at a certain pace and gradually speed up. So I might set it to start at 60 BPM for 15 minutes, and gradually speed up to 75BPM during the 15 minutes. That exercise is helping me improve chord changes. It has lots of other features and it is less than $5 USD.

You mention that the Metronome on GT doesn't keep time accurately. That sounds like it has to be network latency to me. I can't imagine the metronome really being inaccurate otherwise.