That sounds a little dry - do they have any grease in the carriages??

2.7kg also sounds tight - if this is a truck on two parallel rails, i would slacken the screws on one rail, fit the carriage/plate etc and the gently tighten the screws as you slide the carriage assembly along. Also the same for the screws holding the carriages to the plate - slacken and tighten them with the assembly in position. This allows all alignment stresses to be released hopefully.

Still sounds like it needs grease though, my HiWin stuff was very quiet.