DD15 cold start issues

I've got a dd15 (2007) that refuses to start in the cold anymore. I have a block heater working and it's always been good till this fall and winter. It used to start at minus 10 without being plugged in no problem. Now, plugged in I can't get it to start at 0. I've been putting it in my heated shop every night and it starts right up. What do you thinks going on. I'm baffled as I thought fuel was leaking back but if it can sit in my shop for days and not hesitate to start but 3 hours in the cold it just cranks and cranks. Thanks.

 

Just picked a new one up since you told me. I will let ya know tomorrow. But does make sense when ya look it up and the parts guy said yep probably the problem.

 

It does have blowby but not much. Like not crazy but a little yep.

 

Hahahaha probably the problem yep, but it's hard enough to get me motivated let alone have my employee slacking as well..