Make sure the cable tension isn't too tight. One test is that you should be able to pull out the cable out from the firewall -it should only take about 20lbs of foce to pull out the cable about a thickness of a penny. If the cable is tight like a guitar string, there will be less clutch clamping pressure. It may feel nice, but the clutch will slip under heavy loads. I learned this the hard way.
Sometimes when you correctly set the cable tension, the pedal position where the clutch engages is bad (e.g.,right off the floor). If that happens, then the clutch won't completely release, and it'll be difficult to shift.
One remedy for this is to use an adjustable cable. I never used one, but I hear everyone complaining that all the aftermarket adjustalbe cables suck, and you should use OEM.
Another remedy is to use a double or triple hook quadrant. I have a UPR, but I still had a problem with adjustability. On the middle hook, the cable tension was way too tight (even with the adjuster all the way into the firewall). On the 1st hook, the cable was so loose, I had to have the adjuster loosened all the way out to the edge in order to take out the slack.
Good Luck
