Let me make sure I understand your problem. Are you saying it actually hard to put into the lower gear ( like a bad synchro ) or once you put it into gear and let out clutch the car jerks because engine speed and road speed don't match with the selected gear
with the lower RPM ? Was it always like this or did problem just started happening ??
There really isn't a road speed since you could be going from 4th to 3rd or 3rd to 2nd or 4th to 2nd it's really about matching engine speed with the road speed
in lower gear.
I assume trans oil level is good , what type of oil are you using in transmission ?