Transmission Shutter Starting out

I have a 1992 Grand Prix. 3.1L. There is a nasty shudder when I start up from a stop. No other problems with shifting - just when I'm starting out. Does it in all forward gears except when I start out in 1st gear - no shudder then.

Any suggestions on what it might be?

you have a shift control solenoid sticking, and when you have the shifter in drive, it's not downshifting into first gear, and you're taking off in a higher gear. When you put the selector in first gear, you are forcing the valve body to downshift into first, eliminating the shudder. I woudl try a good trans treatment like seafoam or trans-x, and see if it fixes the problem. IF not, you need a shift solenoid replacement.