if you are cruising in 4th gear at a low rpm 1500-2000 then stomp it. Watch the rpm and mph guages. If the rpm guage increases pretty fast but the mph guage doesn't keep up like it should, it is slipping.
The shudder is probably clutch chatter. That's normal for some clutches (like the Spec Stage 3+) but not for others.
The engagement point being high in the pedal travel could signal a worn clutch or it could be a clutch that is out of adjustment. Try adjusting it so that it grabs 1/3 through the travel and is fully engaged by about 2/3s. (I don't know how to do the adjustment, unfortuantely--just know that it can be done. My mechanic got my clutch adjusted spot on so I haven't had to mess with it.)