Digital BW, The Print

I have prints that are coming out odd sizes-maybe 1/2 inck shorter on 
one side, plus the added visual of banding. I took it in and the guy 
said it was fine.All the tests he did were with very thin inkjet 
paper. He said maybe my paper is too thick. I've moved from 310gsm to 
250gsm and now to 190-188 gsm which still has banding and off size.I 
can't go below this weight of paper! What should I do? I've printed 
on two other 3000's which did not have this problem.