I'd suspect initial editing to be a sore point.
Be as exact as you can on including the exact amount of samples (time) as possible .. yet make each edit cross the zero line (or close) to avoid any clicks/pops when the loops actually, um, 'loop'.

Once this basic looping understanding is accomplished, then it comes down to pitch change and tempo issues.

You want to loop the first click (in a given measure) of an audio file to the last click of the desired ending measure. If loops aren't edited correctly they get out of time successively. By that I mean if the loop is one click off, that one click adds up each time it is played. By measure 30 you are in trouble.

That's a lot of what makes RT's so impressive. Not only is the recording done, but then a multitude of loop marker options are correctly applied. It's a lot of work to get one 'right'.

Make your sound your own!
.. I do not work here, but the benefits are still awesome