IMHO, Timbren's are a rough ride when unloaded and the axle makes contact.
Sumo Springs are a better ride, they're always in play.
Air springs even better as they're tunable for load. That said, I don't know what bag options are available for 1500's. For those that off-road in the 2500 HD's they're all using Daystar cradles to decouple the bags on the bottom end.
I had a very poor experience with sumo's on my half ton for exactly that reason, they're almost always in play but, not always. On my truck I had about a quarter to half inch air gap which meant any bump on the road hit hard when the springs contacted.
The timbrens have more air gap, they'll probably hit hard too when they do eventually contact. But it depends on what you're towing, because on most TT's I bet the timbrens are always in contact so it's not jaring, and unloaded there is probably enough gap so that you never feel them.
If you find that perfect trailer/load where it doesn't contact until you hit a bump, still going to be annoying.
I tried the cheap air springs, the airlift 1000 and they also changed the unloaded ride quality until I had them at about 3 psi at which point they were squeaking and rubbing in the spring. They also don't lift anything, they only make the coil spring stiffer by making it harder for the coils to move up/down, whereas true air springs actually can lift the back end up.
In the end I ripped all that stuff off and I'm back to stock. I do get a tiny bit of sag but I no longer care, my truck is working and it looks like it as well, not concerned about it. And the funny thing is after moving to my anderson WDH I've actually fixed the problem I was trying to solve with the springs and air lifts (getting rid of the rear end porpoising).
Probably more then one solution here, better air lift systems or better coils/shocks would work too but I absolutely did not want to change my factory unloaded ride quality in any way.
