I just bought a 2000 3500 4x4 with the NV5600 and absolutely love it. It has a 3. 55 rear end and a gear vendor unit, along with a compression brake and some other mods/bombs. I drove about 400 miles to get it towing a trailer, and put my truck on the trailer and towed it home with the new truck. The load was probably about 8000lbs. It performed awsome, but I have some questions about the gear vendor. First off, it really only seems useful in 5th and sixth. Otherwise it doesnt seem to be splitting the gears. Secondly, my friend who I let drive used the compression brake in 5/over only once or twice for just a few seconds by accident. Will that cause any real damage? Also, I pull the knob up, wait a sec, then clutch and it shifts ranges real smooth. Otherwise I feel like I'm on the clutch for 3 seconds. Any problem there? I like the unit, but i'm not sure how much I trust it. How HD are they? Oh yea, any damage by not clutching for normal shifts if it can be done smoothly? Sorry about such a long post. JOE