PROBLEM SOLVED! (I think) New divider plate, set to .030" or less clearance. I used the stainless steel plate. I think the regular steel plate would have been easier to work with. This was pretty stubborn.

It was a cooler day today, but it ran at 190 on the highway and 195 in town. I just hope I ran it long enough that my result is accurate.

Thanks to all who offered their knowledge and advice!