89 gp tachometer reads too high

My 89 grandprix, 2.8, 5 speed manual tranny.has some tachometer issues.if I'm puttin' around in 3rd or 4th gear,30 to 40 mph my tach is redlined and shift light stays on. could this be my ignition module? since that is where the tach signal comes from, right. Can someone tell me if I'm crazy...well nevermind that..You guys are great and I know you'll have the answer...thanks guys