Evinrude Tilt/Trim Trouble

[Stan R]

I am having trouble with my tilt/trim when I load my boat. With the motor slightly raised if I apply power to get it on the trailer it will slam all the way down. It seems to work just fine out on the water and doesn't sag when I am fishing with it up. Is there something I can do myself to fix this or is it replacement time?
1986 150hp Rude VRO