This may be a stupid question, but how do I know exactly which transmission is in my truck. And how do I find out which input and output size it has right now stock. And how do I know which transmission I can switch into this truck to make it a manual instead of an automatic. It's a 2001 automatic s.o. thanks

 

It is a 47re transmission. The easiest manuals to swap in would be the two you could get from production that year - the NV4500 or NV5600.