Digital BW, The Print

I'm trying to print transparencies, but they always end up 
inconsistent, often with lines or bands in them. I print the same 
images on paper and don't have this problem. 

I'm guessing it may be how the printer "grabs" the sheets, and maybe 
with the transparency film there is some wiggle, so printing is 
inconsistent. ??? 

I've seen some transparency films that come with a white paper strip 
down the side. I wonder if this is to help the printer grab onto the 
film? 

Any suggestions for how to deal with this? And how do people make 
digital transparencies with this problem?  

Best, David.