Thank you all for your wonderful suggestions. No word from the mechanic
yet - he hasn't looked at it yet. This is actually the fourth time I
have been back there this month about the new clutch (once before for
slipping and twice for clutch pedal not springing back completely (O.K.
now) - each time he went to the floor pedal to make adjustments on what
he says is "a wierd clutch pedal setup"). The mechanic was puzzled 2
days ago when I returned again and explained that the new clutch he
installed slips ONLY after ten miles, yet when I went back yesterday to
review with him all of your thoughtful posts he said "I never needed no
internet to fix a car" (sigh). I think he agreed to try and bleed the
hydraulic system first cause your suggestions that the cause may be air
in the lines that heats and expands after ten miles is a great
diagnosis and could be explained by a sloppy clutch installation. While
there I started it up cold and then pressed and released the clutch
pedal 30 times to try the suggestion re pressure buildup from multiple
uses of the clutch. I then drove it (still cold) - no slipping until
5-10 miles of driving. There is no visual leakage but still could be a
problem with the hydraulics - (?? cylinder, plunger, or whatever all is
involved). Maybe the clutch is overheating due to poor installation or
wrong parts. The clutch fork had snapped and was replaced at the same
time.

All parts should hopefully be stock - this ain't no race car (though my
black Dodge Stealth is pretty and has PA license plate BATM0BL). Total
cost = $900.00. Clutch kit = $262; Clutch fork (was snapped)= $71;
Resurface flywheel = $75; Labor (5.5 hours at $75/hr) = $412.50; Shop
supplies = $11; PA Sales Tax = $50.

Will repost once it is fixed and no longer slips after ten miles.
THANKS AGAIN!!!