There are patches for this.....but for longer messages I think it is better to compose your message in word, hit control a then control c and paste into your message box with a control v.
Word automatically self corrects.
Have you tried using one of the Speech Recognition programs? Dragon Voice Recognition software works well and continually self trains itself. The initial setup is about 30 minutes of training, but after 20 or 30 hours it has you down pretty good....and very easy to correct mistakes....