Starts about 45 mph and gets worse it's like the hubs are staying locked in are something anyone have any ideas 2006 f-150 ?

 

First thing I would do is go all over the lift again and double check that everything is secure and tight bolt/nut wise. What may seem like it's tight/snug to you may in fact not be? I would have to think that this is the issue. If not, at least you have piece of mind that the lift is secure.

 

Where is the vibration felt? The floor? The front end? The rear? I had a vibration with my Rize 8" and I ended up replacing the driveshaft with a longer one and it solved my problems.

 

Had a Vacum leak at one of the hubs they where running ingauged went out and bought Ind. type heat shrink with inner glue and repaired lines.. All is well will post picks soon ..

 

Could very well be like Thumper said a drive shaft issue. If you haven't messed with the driveshaft then you need to take out the front driveshaft, have the master spline cut out and rotate the end so both ends are the same way (may not have to do the rotate on 06), lengthen to 37.5" and have the driveshaft balanced. 8" lift isn't tall enough to get crazy with the driveshaft just some mods and it'll be ok. We had a Mark LT we lifted 14" and had to build a dual velocity driveshaft for it but you're not tall enough for anything extreme like that. Here's a pic of the Mark LT we did.

 

I didn't even need to mess with the front driveshaft, it was just the rear driveshaft.

Plus, I didn't feel right having the driveshaft stick 2" out of the transfer case. .