I do suggest buying quality strings and cables. But string stretch isn't causing you to lose draw weight. When strings stretch you actually gain weight. The longer length makes the draw cycle longer which in return makes the draw weight increase. If in fact it is losing draw weight check the limb bolts. Could be they are backing out with more frequent shooting. If you don't have a set of bow scales, take the bow to a pro shop. Check the draw weight. Put the d.w. back to where you want it. Take some white out and make some marks on the bolt and on the limb, not on the washer under the bolt as this thing can turn independent of the bolt. This will tell you if the bolt is moving.While you are there ask the pro to check and set timing on your cam/cams.Also check the brace height, doesn't matter if it is a single cam ,brace height is to be checked. If it is a single cam get a long piece of dental floss, long enough o go from axle to axle. Wrap one end around the axle and stretch the string out and secure the other end of floss around that axle. Now measure brace height. Should be really close to even. But my thinking is telling you don't have a problem but are building yourself up to handle the weight better. Which is a good thing.