What drives are you using? I had some cheap TB6600 drives with 400 oz in steppers on my PM-25 and the drivers were definitely falling short. I was using the same on the Z axis and it would struggle and occasionally stall, especially at lower speeds. I switched to a DM-860T drive and it made a world of difference. Even with the 400 oz in motor on the Z, it would move it just fine up to 150 IPM. I got the same type of driver, just a few sizes smaller for the X and Y and that helped quite a bit. I can run it with 3 4" vises at 150 IPM with no problems.
It is possible that your gib is not sitting correctly. When I put the gib in, if it doesn't wiggle into place just right, it is very tight and doesn't allow the table to slide right. When you wiggle it around a bit and it finds the sweet spot, I can crank it down and the table still moves smoothly, even to both extreme ends of the table.