Dumb tranny question...

well, at least to some it might be. trans and shift kit were on the car when i bought it and i don't know much about automatic transmissions so here goes...i have a small block 727 with a shift kit...problem is when the car has been sitting a while and i start it, i need to shift the tranny into neutral in order to get fluid to flow.

if i don't do this i can shift into any position and the trans will not “lock” into gear. the longer the car has sat the longer i need to wait. The previous owner indicated the stall converter was the problem but i’m wondering if maybe something went wrong with the shift kit install and is maybe blocking a passage? Anyways, it's really just a minor inconvenience but before i start chasing a ghost i’m wondering if i should pay a shop to have a look or just go out and buy another trans...i thought maybe someone here might have any idea where to start...

thanks