I have a 1988 Volvo Penta model 275 outdrive coupled to a GM 5.0 305 cid. Everytime I put the boat in reverse, then move the throttle back to neutral then to forward gear the shifting is hard, however, once I put the motor back in neutral and then move it into forward gear again the shifting is smooth. It only shifts hard from reverse to forward. Is this normal? What could the cause be?