Trans not going into OD

I just bought a 2003 Buick LeSabre for a
winter car. Changed all the fluids I could and
took it in to a trans shop to have the fluid
and filter done properly. They said no chunks
or metal shavings in the pan, but when they
tested it on the hoist, they said they could
not feel it go into OD. When I drove it after
that, I could not feel it either. Is there a
button I have to push first, or could it be a
shift modual.?  Around town it would be fine,
low speed, but there will be times when I will
have to travel highways to VA Hospitals this
winter. HELP