MSD GRID

Anyone having a problem with their Grid not shifting where you set it ! For instance settings: looking set at 7000 shift point 7400 . Run the car down the track it shifts at 7600 ! So we change it to another setting , but still the same thing! Doesn’t shift where we want no matter what ! We can get it to shift at 7400 but we have to set for instance looking 6800 , shift point 7200 and it will shift at 7400 . Non of that is right ! Called MSD tech. Tech said to put a diode in the yellow tach wire , and move the tach wire away from other wires ! Then it should shift on point ! Anyone experienced this ! We are new to the grid , so we are pretty green !