Lime GT

I've been noticing what I believe is a driveline vibration in the 45 to 60 mph range when I'm in 5th gear. I have FRPP 4.10's installed and they're dead quiet. This vibration sort of thuds the car as well as the steering wheel slightly. Now that I think of it, I believe I had somewhat of a vibration before the gear change in the 55-70mph range but was hard to tell because of the wind noise, engine noise, etc. at those speeds. I'm wondering if it's more pronounced now due to the lower roads speeds as well as being in the 1600 to 2200 engine (droan) rpm range. Anyone else notice this with 4.10's? Maybe it's a u-joint starting to go but I doubt it as the drivelines quiet when loading it as well as only 28000km on it.

I'm thinking of going to the dealer but after my last visit where they claimed my heater distribution is normal and my loose rattling dash louvre's are normal, I think they'll probably blame this one on the gear change.