captain: Oil pressure variation is normal from idle to WOT. Actually, it'* recommended, I wish mind did it :(.
Your motor COULD be shot. However, since you must hit it, that sounds like it'* functional, but there is a wiring issue. My window speeds always increase when I use two switches [master driver'* switch, and the window I am moving. Try that, if it helps, it'* probably wiring. If it doesn't help, it very well could be the motor. I say if the double switch thing doesn't help, try testing the voltage at the motor, to make sure it is getting proper voltage, and doesn't fluctuate much. If everything is fine going up to the motor, it'* probably the motor.
'89 SSE - GX3 -190k, 155k on body - Back for another ride.