I have a 2002 volvo penta dp-s outdrive giving me a problem. when i try to go forward i have to rev the engine up to about 1200rpm and wait about 30 seconds before it will go into gear. going into reverse works perfect. i have adjusted cables, pulled the shift shoe for inspection and i have changed to oil. after changing the gear oil it worked good for a while and now it is starting to act up again. thanks in advance for any help.