Tom-I specialize in Chevy Blazers and GMC Jimmies and when they exhibit
the symptoms you describe, its  the motor.  Have one ready when you
tear the door apart.  I would unplug the old sleepy motor and plug the
new(or re-man)one temporarily(in your hand), then activate the power
window switch.  One way for approx. 5 seconds and then the other way
for 5 seconds or so.  If it works both way without stopping or delay,
thats your problem.  Of course it could possibly be your live feed or
ground issue and even possibly the power window switch but my money is
on the motor.  Try this technique but use care around the window
sissors, etc.  Also it wouldn't hurt to have a manual handy as you'll
need to more that likely duct tape the window in the up position,
remove the factory rivets holding the motor in place(or nuts and bolts
if previously replaced)and guide the old motor out of its spot(usually
tight) and sissors out of window tracks.  Anyways-good luck!jp

I believe there is a circuit breaker in the power window motor circuit, but
I am not sure where it is located on your vehicle. When an electric motor
gets in a bind and can not turn as fast as it should, the current draw on
the motor circuit will increase. The increased current is probably tripping
the circuit breaker and of course after it cools down it resets and the
circuit works again. You need to find out what is causing the bind on the
window motor. It could be that the window is binding in its track or even a
problem with the motor itself. Maybe even the window regulator needs to be
lubed..

Sounds more like a bad gm connector - normally a gm power window motor
either works or doesn't work at all - gm connectors are notorious for
cracking in hot weather!! Your problems will the connectors location!!