1994 G20 axel issues?

I have a really odd, and for me hard to figure out problem. This maybe transmission related or axel or driveshaft bearings. None the less maybe someone else has experienced this: van runs and drives fine, your just about to switch out of first gear or maybe second going about 25 miles and hour or less and inside the van it feels like the van has been thrown in first gear and the whole thing jerks back then runs out fine? This vans had this condition most of its life and it is time to narrow down possible causes. So if your van has ever done this please tell me what it took to fix it, or at least give me some suggestions to try to hunt it down............................:banghead:

Shift to second or low gear and see if it does it.
If it only does on the 1-2 shift would be checking for transmission shifting or engine mount problems.
MT