Be dead straight and dead level truck to 5th wheel
Chock the rv wheels.
Raise the 5th'er until you see a sliver of daylight between the plates of the hitch head and the pinbox.
Back into the pin slightly- Set parking brake while backed into pin.
Lift and pull handle.
If it doesn't release, you can take a long crowbar and while someone is pulling hard on the handle, bump the jaws.
I have taken a 5lb sledge on a crowbar and smacked the union where the jaws meet. It released violently.
You can remove the pins and lift the hitch head off the pullrite slide part. This may allow you to get better leverage on the release mechanism
Alie & Jim 2009 CarriLite Max1
Volvo Dually Pickup
My keyboard is faster than yours