How does the luff tape look? If it's worn, a new one is much smoother. A a small diameter static halyard is definately best.
You could also check the distance from the plastic batten end-stops to the boltrope. If it's too tight, you could get a lot of friction there.
I agree with Jake about what parts of the sail takes downhaul loads. Forces travel both along the luff and the boltrope, but the major part is transferred to the boltrope.
When installing a boltrope, it is customary to push the luff tape/sail up a few centimeters before stitching the boltrope to the tape/sail. Done this way, you will first stretch the rope, then the cloth, before all the rest of the forces are transferred to the bolt rope. Earlier sailmakers was really picky about their boltropes, as stretch characteristica would differ between ropes from the same batch.
Try pulling on a piece of cloth similar to what is used in a standard mainsail with a 16:1 downhaul, and watch what happens <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" /> (it will stretch)
There are 10.000 denier pentex tapes available which can be installed in the luff of mainsails. This tape is strong enough to take downhaul loads instead of a bolt rope, and might be a good idea if you are using very light cloth in the luff area.
Downhauling bends the mast becouse most of us use aft-swept spreaders these days (pre-bend). It's not primarly the cloth that stretches, but the mast bends, moving the lower part of the main forward while the leech loosens.
Just my opinions..
