Ummm... that happened to me too... the engine made a whiney revving sound between shifts.
I noticed that it doesn't take much pedal movement for the clutch to disengage, so I had to let off of the gas much earlier than I used to in the other GM truck I drove for 12 years.
So, push the clutch in slower, let off the gas a little sooner. I know, it sounds too easy, but try it yourself and see if you notice that it stops... it did for me. (it still happens to my husband when he doesn't move the seat back a notch before he drives it)
