"88" C-3500 auto Transmison

The truck is a 1988 c-3500 with a std. 3speed auto tranny I think it's a T-400 Thats just a guess deing disabled it's vary hard for me to get under the truck. The trouble started when the tranny started leaking fluid from the front cant tell where exactly. But after about a week the tranny started to slip and now she don't move at all. I never let the fluid level get to low. I was told many things that could be wrong , torque converter, valve body pump, bands, Could someone give me there best guess what might have happend. Thanks Bob

Ok this is strange after 2 years of sitting dead the darn thing is working again. still slipping but it is moving crazy i don't get it.