Hi guys im new to this site so hopefully this comes out ok ,I recently bought my first range rover [4.4 vogue se 2003 lpg converted ] and found that as im driving when I approach 25-30 mph the vehicle begins to shudder ! but if I continue accelerating and pass this speed the vibrations stop, ive had a quick look at the propshaft on inspection the u joints look ok relatively new. Is it possible the shaft has been taken out and put back in the wrong place and is now unbalanced ? or do I need a new shaft ? hopefully its not a gearbox fault , also if I drive in manual the shuddering does not happen ! any help would be much appreciated I look forward to hearing ideas

 

It's crazy but a sticking brake caliper could cause this. I know sounds crazy. I would look at brake pads for over.
Heating
That's all I got I hope it may help.
Good luck