oh dear. This is a common problem for me on all printers. years and years of 14x17, then one little bitty letter size, and the printers (which are designed for that size) just cant hack it.
wheres the jam? does it make it through registration? Or, do you share my problem where it goes crazy in the stacker? And it Looks like Stevie Wonder stacked them...
I just went through my igen and cleaned EVERY roller AND sensor I could reach. Use alcohol on the rollers.
check fuser picker fingers(skives, in Kodak-ese)
open up those doors and watch it run, maybe spot a bending corner, or paper skewing.
Also, ever try to run 8.5x11 SHORT EDGE FEED? might work in a pinch.
another bad spot is the fuser exit. certain sizes curl down post-fusing, and catch on the little louvered "ramps"