Is the cylinder smoking hot after all those rounds? Have you tried removing the cylinder and cleaning it? You may need to use a high temp lube
Here is a good post on disassembly
http://gunner777.wordpress.com/2008/08/24/ruger-gp100sp101book-of-knowledge/
Here is a good post on disassembly
http://gunner777.wordpress.com/2008/08/24/ruger-gp100sp101book-of-knowledge/