You dont mention what voltage. 36 volt can last 8 hrs, not a 24 volt truck. A/C motor lasts longer, DC eats more battery time. Type of battery makes difference. I've seen a load of batteries arrive new, same type and volatage. Some will never last 8 hr shift and always give shorter work times. 6 hours might be normal if the truck is run non-stop. If you have two trucks the same, are the results similar with battery in each truck? Or different batteries? If not, ask for warrantee on the new battery.
For reach cylinders, the old Easi reaches always hit hard. Make sure the bumpers are in place and each cyl is adjusted evenly. Setting the reach to 2-speed can help. With 2 speed, You need to push both buttons one after the other to get fast reach or retract. Letting go one button slows the retract down so the banging and load shifting is not so hard. You need access to Superword to change settings and must know the code for Superword