1996 Trans Problems???

I have a 96 winnie with 3.8 in it.The car is very weird.The trans does not like to shift when first started but if you take off in 2nd gear and then shift to drive the trans shifts great until you shut the van off but if you start off in 2nd again it is fine till you shut it off.I can drive the van 100 miles without shutting it off and it is fine but once shut off i have to start all over again.Is there a sensor i can check and replace or is it a bigger trans issue?Thanks