Is there a way to tighten up neck tension with lee dies?
Collet for full length sizing die?
If it is the collet die you can either purchase a reduced size mandrel from Lee or reduce the diameter of yours buy chucking it in a drill and using sandpaper. But, if the brass you are sizing has been sized many times and necks have work hardened, you need to anneal the necks.
If it is the full length sizing die, you can reduce the size of the expander. Same process, chuck the decapping rod in your drill and sand down the expander.
You also might try full length sizing your brass without the expander in place and measure the neck OD. Then expand the neck and see how much you are expanding it.
Lots of folks have trouble with the collet die. You MUST read the instructions and follow them or you are going to be disappointed. I use them for all my rifle calibers and have no problems at all with them.