If the seal is OK
Check the anti-cavitation valve.
Located below the output port cylinder.
are often damaged seats.
Replace section tilt and AUX first
They are the same.
When the tilt spool is actuated to the tilt forward position, the open
center flow path is blocked off. This forces the oil through the load check to the
high-pressure bridge core and is directed out the work port to the base end of the
tilt cylinders. The oil from the rod end of the tilt cylinders returns to the opposite
work port and is metered back to the tank passage through orifices in the tilt
spool/tilt lock piston.
An anti-cavitation valve is utilized in this circuit, which functions. The maximum pressure of the tilt function is limited to the
secondary relief valve pressure setting. When tilting back, the open center flow path
is blocked off and forces the oil through the load check to the high-pressure bridge
core. Oil is metered across (feathering lands) notches in the spool before flowing
out to the rod end of the tilt cylinders.
Hydraulic Systems
The upper load check prevents backflow from the tilt cylinder under heavy load
conditions. If the load check was absent, under a heavy load condition the mast
could drift forward until the pressure builds to a sufficient level to move the mast
backward. The oil from the base end of the tilt cylinders returns to the opposite
work port and then to the tank passage. The maximum pressure of the tilt backward
function is limited to the secondary relief valve pressure setting.

it sounds like the coil opening pressure or lack enough

i will do that monday. lift and sideshifter works good. the truck will tilt good and will stay in place , untill you try to till back some more , it starts to crrep forward.then stop when you releas the lever. and if you give it gas and tilt back it will titl then starts to creep forward when you take your foot off the gas pedal.

beginning with hydraulically pressing test
best regards michel