My speedometer is intermittent as well as the tachometer. Sometimes they work well; sometimes not at all and sometimes one does and the other doesn't. A mechanic said it could be my speed controle module, or speed sensor...but what about the tach that should be coming off the transmission? Please someone with valuable knowledge help me out. Thanks!

Actually, l think you misspoke as the tach should come off the engine and the speedometer off the transmission. They may both go through a speed control/speed sensor module and are affected that way. l am guessing it may be time to replace it: the car is 15 years old and things start to fail. You might, if you have not already, pose the question on the Lexus Owners forum at: http://us.lexusownersclub.com/forums There is an even wider range of knowledge there.