Actually it probably isn't the motor.  There is an inter lock switch that
will not let the window go up unless the gate is closed completely.  When
the switch goes bad the window goes down but not up.  Open the gate, remove
the trim cover, remove the steel plate and on the right side (inside the
gate) look for a switch bolted to the passenger side lock.  Pull off the two
wires and with a paperclip short them together  Then reach under the
tailgate (with it down) and see if the window now moves.  If so then the
motor is ok and the switch is bad.  You can get a new switch for something
like $13 from GM or just connect the wires together permanently and tape it
to the inside of the gate away from the window.  This switch is a common
problem.  I have seen it go bad in every blazer and suburban I have seen.
The only catch, once you jumper the wires together you must make sure the
gate is closed before closing the window or the glass may shatter.  Mine is
jumpered....  For the time being open the gate and give it a good slam, if
it works then it is the switch.

If you do need to replace the motor then it is easy.  Once you remove the
scissor sliders from the bottom of the window it will slide out easily.
Just be careful the glass is worth more then the truck.  The local dealer
here has a 1/2 ton 4wd 91 suburban for $950.  Just kills me.  Should be
worth more imho.

Good luck,
mark

Thank you I will let you know..

Al