Hi
As I understand it...transitions between clips work OK...yes? However I am not too clear on what you see happening with the text you are adding, particularly when you say ".in the final product it takes longer and longer each time and its covering up important parts of my video." What is actually taking longer and longer....the duration of the text???
Under normal circumstances If you place an image, (e.g. a png) between the clips (on Video track1) it will behave like an inserted video clip and you can add a transition to it in exactly the same way as a clip.
The difference with an image (text or otherwise) is that you have to set its duration by changing the default value under "Options/Media". (You can also change the duration of an image by simply grabbing and pulling out the ends along the track.)
Another difference is that when placed on Video track 2 there is not normally a following clip which means if you add a transition to it, the WHOLE transition duration will be added to the text clip. (Normally it would be divided between consecutive clips.)
The default value you have set in Options will also apply to your text image as well, which will automatically be placed on Video track2 as an overlay, although you can move it down to a lower track if you wish to.
If the text image happens to be of longer duration than the image beneath it then it will spill into the following clip.
Provided you haven't changed the duration of the text(s) they will all be of the same length.
Under normal circumstances what is previewed is what is exported.
Post again with a bit more detail 
Nat