However many times when I use keyframes to make the text come towards the camera on the z axis, it makes a small loop instead of coming straight forward and it changes the x axis even though I didn't touch it. Anyone know what I am doing wrong?
You are probably manipulating a 2 node camera instead of your text. the camera moves forward to the point of interest and then flips over to the other side. you can manipulate your text instead of the camera, or manipulate your camera properly.
The other issue is that lately my compositions won't RAM preview or can't be played back all the way.
Ae will give you as much RAM as it can, based on what's available. you do have to check your preview settings so that you are getting the behavior you want. for example the range: if the work area is trimmed, you will only preview it's timespan when this is the option in the Preview options.
I tried the cache before playback option and changed range to work area and it seems to render more quickly.
As far as the text goes I am pretty sure it is just the text position I am changing. Sometimes the text will come toward the camera and other times it does that small loop thing I mentioned.
show us the loop thing so we could see what exactly is happening. Either of these will do: Screen shots/video capture/rendered video/project file