1999 Bravada problem

Hi All,
Looking for sone advice ona a 99 bravada that my son and daughter and law have. She was driving tonight and came to a sto and when she gave it gas to go it would'nt go. She put it into 2nd and was able to go and made it here. My husband got in it and found that you had to start in 2nd and it would shift up to drive and be fine. ( Its an automatic ) So she headed home doing it that way and said then she decided to try it again , stoping in drive and taking off in drive and it worked,,,,ummmmmm,,,,, any clues? Thanks:banghead:

I think the Check Engine Light should have come on and a transmission diagnostic trouble code generated. You might check and see if the transmission is full of fluid.