I would think your LPM is an issue, although related your pressure would be ample for the "tonnage" that you are operating. The other thing to consider is the springs in the hand valve-Ie the two springs either side of the spool operating the valve from left to right. If that slides over too slowly, the pressure from and to your ram will cause it to be too slow-this will in turn slow your flow rate down. A stronger spring or spacer may help with this.
Even mechanical springs directly on the ram would help if correctly placed.
Not to detract from the wonderfull work you have done, why did you go for a 12V pump and not taken power off the motor, as in a power steering system on a car ?