PB G4, 15" - Cursor Jumping Around

I have an A1095, running 10.4.11. Recently changed out the top case due to poor performance of the keyboard and trackpad. The cursor jumping around problem existed before I changed out the top case - AND, it's still a problem. It is most noticeable when answering or composing new e-mails. The cursor just takes off and may end up anywhere, i.e, into the body of text I'm composing, or maybe down into the body of the received text, or up into the subject line, etc. There's no set pattern, the darn thing just goes nuts and drives all over the place, AND, I have to go chase it and bring it back into my text body. It's driving me crazy. I should tell everyone, I dropped this notebook off a table onto a concrete floor when my dog got caught up in the powercord, in my garage office. But this happened a couple months ago, and the cursor issue just emerged about 10 days ago. Thanks for any help anyone might be able to provide.