01 Tranny acting up

I have a 2001 Chevy 3500 4x4 with no after market additions. Has about 52000 miles on it. Every once in a while if I have to make a hard stop while under a load (example-car turns in front of me) the transmission will not shift right after that and if you shut the truck off and restart it, the trany works fine. I have noticed that when this happens the battery light will come on, service engine light will come on and the battery gauge will be reading about 10-12 volts if not lower. The gear shift selector light will be blinking on and off and the truck will only move a little bit maybe at 5 miles per hour if that. Most of the time I have to stop in traffic and shut off the truck and restart it. After a couple of start ups after this has happened the servcie engine light will go out. Any ideas. Would like to have an understanding before I take it in to have the codes checked. Could this be a bad battrery, alt. of serpentine belt. I have noticed that when I start it up the battery gauge will hang about 10 volts for about 30 to 45 seconds before it goes up to 13-14 volts. It doesnt matter what the temp is outside, or what the trany temp is. Will do it cold or warm.