BoatBanter.com - Trim Woes

Took the boat out today and ran into some problems with the trim. The
motor is a 1993 Evinrude 140. Let me see if can describe each of the
behaviors that I experienced.

Boat out of the water
======================

Tilt/Trim (up and down) on the motor works fine.
Tilt/Trim (up and down) on the throttle control works fine.

Boat in the water with engine off
================================
Tilt/Trim (up and down) on throttle control works fine.
Didn't try Tilt/Trim on the motor.

Boat in the water with engine on in neutral
===========================================
Tilt/Trim Down on throttle works fine.
Tilt/Trim Up on throttle results in runaway trimming up about 80% of
the time. I have to press Trim Down repeatedly or hold it down to get
the motor to stop trimming up.

Boat in the water with engine on in gear (forward)
================================================== =
Trim is down as far as it can go. Driver engages the throttle to
accelerate. Before the boat makes it on plane, the engine begins to
trim up about 80% the time without any interaction from the driver. I
have to press Trim Down repeatedly or hold it down to get the motor to
stop trimming up.

Boat in the water with engine on in gear (forward) at speed
================================================== =========
Boat is on plane with good trim setting. Trim begins to trim up
unexplicably every minute or so. I have to press Trim Down repeatedly
or hold it down to get the motor to stop trimming up. Once the
trimming up has stopped, trim down works fine. The slightest tap on
the trim up switch, however, causes the trim to runaway again. I have
to press Trim Down repeatedly or hold it down to get the motor to stop
trimming up.

Also, the trim gauge does not seem to operate properly any longer. It
usually does not accurately reflect the position of the trim.

Any help with this problem would be greatly appreciated.