Got any pics?   

Any windows in the ends?    Ever consider adding a very short addition onto the exhaust/fan end?  Even a simple 8' single slope addition that allows you to mount fans does the trick and cheaply.  

Air does not need to travel straight line.... yes, that 's most efficient , but, an 8x8 foot square opening is 64 sq ft, and if there are any windows, could quickly got to 80 sq ft, and a 48 " fan is only 12.56 sq ft.... so effectively, your doorway alone is the same as 5 fans, and a couple small windows would add the same area as another 48" fan.  

We did this on our old stall barn, 25 years ago.  Many fans were also placed in the haymow, and ducting was created.  

Just something to think about

Hands down, Pulling air wins.....