Try to run a set of films through the stock Epson driver, then run the same through Wasatch, just to eliminate if it's a driver issue or not. If the films turn out the same, it might be a mechanical issue, or it might mean that the Wasatch RIP uses the stock drivers.
I switched from stock drivers and Ghostrip to Accurip, and Accurip gave WAY better registration results.
Also, if using roll film, unroll it a bit and let it run through the printer with some slack. Also, check that the roller spindle moves freely.