I have a 2005 dodge cummins 2500, just installed a 6" tuff country lift. i still have the stock rims and tires. The truck shakes vilently after hitting small bumps at 70 mph. Tuff country claims it's because i have small tires but really???? What is the cause???

 

Assuming your track bar is in good condition I would replace the steering dampener.
I've seen lots of them develop a soft or spongy spot in the straight ahead position even with no fluid leaking.
You did get an alignment done after, right?

 

also, when you get the alignment done, get the caster set at 5.2 or better on each side. this will help with the DW problem. just make sure your pinion angle is not too far off otherwise you'll have bearing noise & wear.

 

first off a steering dampener can cause or fix it. All the dampener is for is to keep the steering wheel from taking off fingers when hitting every bump. If the steering is set up correctly then a dampener isnt needed. He is still using the same dampener as he had on with the stock suspension. or a new one if it came with the kit. so would it make sense that another one would fix it. no.
Being that it started after a lift I would say you have steering geometry issues.
your drag link has to be parrallel with your track bar. check the caster as well like steve-o said. did the lift kit come with a trac bar? or a lowering bracket or something?
how is the center position of your axle? if it isnt centered it can cause some issues (only fixable with an adjustable trac bar).
dont buy a steering brace either. that is another bandaid thrown at death wobble.

 

I have this same issue with only a leveling kit and 315-70-17 bfg a/t.. Steve been a while since i have been on. I had my truck aligned, and my caster was a 5.2.. He said that was all he could get,he did make some adjustments to the tow so he could feel better about taking my money. I still have the death wobble he said everything in my front end looked good and tight. I know you said one time before that the dampner was just a bandaid. could it be a tire issue, I have rotated them, balanced them, and after this last alignment cross rotated the front two. what would be my next move? new tires or a steering dampner. I would like to fix the issue but funds are tight around here but I have to be able to go over 70mph. thanks for your help and time.

 

do you have fixed control arms or adjustable? could your CAB's be worn? or new (I forget). I had issues with my axle being a tad bit to far forward but that did not create any DW issues, just drove funny.

If your arms are adjustable, set the length at no greater than .5". I had mine set there and pulled it back 1/2 turn and it made it better. moving the arms back should not greatly affect your alignment.

when it shakes, is it the DW for sure or is it a shimmy?
is your pitman arm dropped accordingly? the steering geometry needs to be in line as well (hence the pitman arm ?)...