Canner conundrum.

<p>My sweet sister-in-law is due to have a baby soon and I am going to go help out. To prepare I am making some of my usual canned goods to take. I did spaghetti sauce Saturday. About halfway through the pressure all of the sudden lessens and my weight slows. I scrubbed it well and looked it over. There were no leaks from the seal as it cooked and other wasn't looking weird. I figured it was a fluke. Today I put in some tortilla soup. 7 quart jars. The max for my canner.  With 20 minutes left the pressure started to yo-yo. Never changed the heat but the pressure went up and down. Any ideas? Do i just need to replace the whole shebang? Did i do something wrong ? Is there some upkeep I don't know about? It is a presto pressure cooker /canner. 7 quarts. It is not even 3 years old yet.