Could be a number of things. But if the cylinder holds the position once up as far as it will go, then it's not the cylinder.
Could be low oil, worn charge pump, pressure relief valve worn or in need of shimming to increase pressure. The sqwalking/squealing sounds like the relief valve is bypassing the pressure.
But first look to see if the cylinder is extending fully. If it is, then you should hear squealing and you need to look more at brackets/hangers being worn or bent causing the partial lift.