2010 Honda Odyssey with 89k miles, at highway speeds there is a "shudder" in the engine.

We have an older, 2005, Mazda MPV minivan that did this for quite a while. Usually from 40-60 miles per hour, mostly during acceleration but not always. You minivan is probably mis-firing some. Could be bad spark plugs, or plug wires, timing or other problem. Ours was plug wires and 3 of the 6 spark plus were not replaced by shady mechanic, they were in there forever! Are problem varied by season, load, etc so it wasn't so obvious. Your problem could also be the transmission. Could be one gear in the transmission is having a problem.

I have notice the exact same thing in my 2010 Ody. Ours has 172,000km on it. It does the 'bump' thing randomly while driving at constant speeds around 70-100 km/h. I hooked up my scanner/monitor and noticed when the engine does the hiccup the timing goes to 0, then resumes to +35/36 degrees. 35 degrees is common while cruising down a road. Every time it 'bumps' the timing jumps to 0 then back to normal. I suspect it has something to do with the ECO on the van.