I have a 1997 Merc 75 HP on my Nitro 700LX. The trim gauge works fine until after 4-6 hours of fishing then if you stop for a while to fish & get ready to go again, the trim gauge shows 0 tilt, even though you have not trimmed the motor down. But then the next time I go to the lake it again works fine for 4-6 hours & does the same thing. Any ideas?