[cupidstoy]

not an experienced towing guy with the tundra, but this sounds like a harmonic frequency thing to me. i have towed a lot of trailers and the thing you want to avoid is a magical accident of having the bounce of the trailer be a multiple of the bounce of the truck - essentially reinforcing a naturally occuring resonant frequency. don't know exactly how to describe it, but you end up with a natural frequency that reinforces itself. for example the distance between the wheels on your trailer and the axle on your truck may be the same or twice the distance between the front and rear axles on your truck. then, when the truck bounces over a bump, the suspension is just bottoming out when the trailer tires hit it and you get another bounce out if. does that make sense? i'm sure ray or some other expert can explain it better.

i think you have accidentally put together a configuration that reinforces itself. the thing to do is change something that affects the resonant frequency of the system as a whole so you don't get the reinforcement or minimize it. if it's a high frequency bounce, changing tire pressure one or more places might do the trick. if it's a larger waveform, changing the damping on your shocks might do it. if its a really long, loping bounce, you might have to change the location of the axles on your trailer if that 's possible. without seeing your setup, it's hard to recommend a fix. anyway, your post is several months old, so you might have figured out a fix by now.

another possibility is having a longer waveform additively effect a shorter waveform. for example: the suspension on your truck has a natural frequency of .5 seconds when you hit a bump on the freeway at 65 miles an hour. the distance between the rear axle of your truck and the axle on the trailer results in the trailer wheels hitting the same bump your truck just hit only .75 seconds later. now, every 1.5 seconds, you'll have a bigger bounce because it is being reinforced. (.5, 1, 1.5, 2, 2.5, 3 etc for the truck and .75, 1.5, 2.25 and 3 for the trailer).

i realize that may not make much sense but it's the best example i could think of. either way, the solution remains the same. change something in the system so the resonant frequency at your preferred cruising speed goes away. adjust tire pressure on one or more axles, change tire size, change distance between axles, change suspension damping characteristics, change weight distribution, etc. with a little experimentation, you should be able to figure something out that isn't too expensive.

my personal experience with towing is that longer trailer tongues, thus larger distance between rear axle and trailer axle, results in smoother ride. also, distributing the weight correctly makes a big difference.

post an update if you get a chance....