Congrats on reaching rank 55. The reason why it takes longer to move up the ranks is because your reputation rank is a logarithmic function of your reputation points. More specifically, you need to increase your reputation points tenfold to see your rank increase by 9. I believe (but am not quite 100% positive) the rank table works like this:
| Reputation Rank | Reputation Points |
|---|---|
| 79 | 1 quadrillion |
| 70 | 100 trillion |
| 61 | 10 trillion |
| 52 | 1 trillion |
| 43 | 100,000,000,000 |
| 34 | 10,000,000,000 |
| 25 | -1 billion to +1 billion |
| 16 | -10,000,000,000 |
| 7 | -100,000,000,000 |
| -2 | -1 trillion |
| -11 | -10 trillion |
| -20 | -100 trillion |
(EDIT: Just checked and found exact numbers.) A new account begins with zero reputation points.
Yes, reputation works logarithmically as far as I know. Wouldn't it be nice if the developers actually published all this stuff somewhere so that we could all find it easily and know that this is actually how it works and not just what someone believes how it is? You know... an official document!
Thanks for reading and commenting!