<p>Vim is acting slow when I scroll. The cursor skips some lines when I'm pressing j/k continually.</p>

<p>I'm using xterm and urxvt. In both vim acts like this.</p>

<p>This happens locally, with small or big files. I do use Control + F/B they work just fine.</p>

<p>EDIT: ttyfast in small files did the trick but in bigger is the same. When running without customization it goes allright.</p>

Have you tried the 'ttyfast' option? See:
```
```
:help 'ttyfast'
```
```
for help, and:
```
```
:set ttyfast
```
```
to enable it.
Also, what version are you using? And have you tried this with no customizations to see if something you've set is interfering?
Run it like this to omit any of your vimrc settings and plugins:
```
```
vim -u NONE
```
```
EDIT: If removal of customizations fixes it. Remove things iteratively until the behavior returns. Start by narrowing it down to either a vimrc problem or to plugins.