I have read several threads with similar issues, but haven't yet found my exact issue.

I have a 2015 Ram 1500 Laramie 4x4
I just had a 4" ReadyLift suspension lift installed and had an alignment done. I am having a very significant vibration when taking off from a stopped position that lasts for about 5 seconds and then goes away at higher speeds. It rattles the whole truck, but seems to be coming from the front.
The vibration does not return at any higher speeds.
This is occurring in 2wd mode. (I have stopped driving it for now and have attempted it in any 4wd modes)
The tires were balanced beforehand, and there was not even a hint of vibration before the lift was installed.

Readylifts website mentions a vibration issue in Ram, but states that is isolated to 2006-2011 Rams and only in 4wd hi mode.
Any help??

 

Take it back to the installer, show them what's happening. See what they have to say.

 

I did that first, and I quote, "We have no idea, we did everything right. Call readylift."

 

Sounds like they didn't install a drive shaft spacer, it might not have come with the kit and now the splines on your drive shaft might be out too far.