Radio and tachometer issues

Victim is a stock 93 Stealth RT/TT with a 6spd drive train. Car has the stock Mitsubishi radio/speakers. The radio may not be a 93; it has the fancy graphic display. Two issues:

1. Recently had a loss of speedometer issue, speedometer drive on transmission was broken and I replaced it with an identical unit from my spare 95 transmission. Now the tachometer doesn't display the correct RPM in 5th/6th gear. At 64 MPH the tach should read 2000. It reads 1600. At 80 MPH it should read 2500. It reads 1900. While it is a lot harder to tell if the tach is reading correctly in the lower gears, it appears that the lower the gear, the more accurate the tach. The tach is normal in neutral. Connector at trans looks good on both sides. Ideas?

2. Radio has been fine for the 5 years I've had the car. Day before yesterday, display for radio is all normal, but there is no sound from the speakers. CD works fine and has full speaker volume. I-Pod also works through Aux port. Is the likely some connector issue or an internal radio failure. Ideas on how I trouble shoot?

Thanks for any help you can give me.