The breather on the left hand tank (opposite side to where the oil is coming out) is blocked. Remove it to test.

If memory serves me right dont these thrucks have two Hydraulic tanks...one on each side of the truck?.....sounds like you have a resitriction in the one tank not allowing fluid to get back into it and it is going to just the one tank. I think there is a problem with the tank that is filling while running....

i find it odd that it is returning more fluid back into the tank than what it is taking out.
have you checked the hydraulic filter(s)?
i wonder if one is clogged up causing the fluid to back up

just a thought, may not be it :o)

hydraulic oil begins to rise out of tank when you step on pedals even though it is below fill level contact tips are okay

Just to confirm, are we talking RR30xx or RR50xx?? Swoop's answer seems to be relevant to RR30xx machine.

If RR50xx, which lift motor is running as soon as you turn on, the front or the rear? If rear then P2 pump contacts maybe welded shut but Access shouldn't allow line contactor to close if they are. If front motor is running as soon as you turn on and are standing on the foot pedals then thats normal (for steering) but if forks are lifting at this point without touching the multifunction handle then either the proportional lift valve is stuck open or it is receiving an erroneous electrical signal.

More info required really, are you standing on the truck or off it when you key on? Is the line contactor closing? Is oil coming out of the breather or the filter housing? Are you sure the return pipe from the steer system to the filter housing isn't split? Is the black filter housing cap fitted correctly as they can be a real pain to get locked down properly and will leak if not? Is the filter clean?

fluid coming out of the breather/filler cap? sounds like the fluid level is too high. It should just be visible inside the filler tube where the cap screws onto... just up to the screen inside it, any higher than the bottom of the screen and when fluid expands when it gets hot the level will rise and it will come out.

when you say forks going up by themselves i assume you mean the motor is running on its own without pushing the lift button?
lift button stuck or contactor tips stuck?

worse case scenario it could be a problem in the function control board but i'm betting it's a stuck switch or contacts.

could be wrong though :o)