Thanks for the advice, everybody. I did the job today. The road trip was totally uneventful. Even though I was going much faster than I do in the field, the road was smooth enough that the mower barely bounced at all. Frankly, it gets a lot more bouncing up and down in the field than it does on the road, so there you go.
About the only thing that was notable about the trip was an odd left-to-right undulation that occurred at speed on the return trip. It was "phased" in nature, as if (and I'm not saying this is what was happening, but it is an example of what might cause the phenomenon) the rear wheels were slightly different sizes, and slightly out-of-round, so that at one point, they were out of sync and the tractor undulated left to right, and then they slowly moved into sync, and the tractor undulated up and down... and then back out of sync again. The undulation was coming from the rear wheels, or thereabouts--definitely not the front of the tractor, and 99% sure it wasn't the implement swinging around, because it was far too regular for that. I noticed that it only seemed to be happening when the engine was pulling (not 100% sure about this). When coasting down-hill (pedal down, but HST not pulling), it didn't seem to happen. Then, when pulling on a flat, it would happen. I speculated that maybe it had something to do with the diff--that maybe the tractor hadn't shifted out of 4wd for some reason when I took it out of 4wd after finishing mowing. I slowed down and put it into 4wd, which put me in a bit of a pickle. It wouldn't come out of 4wd, so I straightened the wheels and rolled slightly forward, which usually does it. Oops. Since I'm on asphalt, I'm only binding up the diff more. I wasn't sure what I was going to do, until I realized I could just raise the front wheels with the loader, tap the HST pedal slightly, and it freed up instantly. After that, the undulation seemed to go away... but I could have just been imagining it.
Anyway, I'm sure it's nothing, but it sure was interesting while it was happening.
Since I know y'all love photos, here's a photo of my tractor in the field after I finished mowing.