I bought the Dakota Digital SG-8 for the tach and the SG-5 for the speedo. I had a little difficulty with the speedo at first, I ended up setting it so read too high and then pressed and held the dn button until accurate. I did this along side my garmin as its pretty close.

The SG-8 was a little harder, could not get that tach to read accurate for anything. Then I called tech support, they were very helpful. When using a V6 tach with a LS engine, you need to set it to 4 cylinders, go figure! It is dead on accurate with no fluctuations or jumping around. I tested this with a computer plugged in to compare it against the ECM.