I have been experiencing a vibration since new that occurs at varying speeds but only when the vehicle is under a slight load , usually climbing a slight uphill portion of smooth pavement .
I only noticed it at around 40-44 mph locally , but I was on a road trip and it occured again , fairly severely at 65-70 mph over the weekend
The vibration seems to come from behind / under my seat , the steering wheel does not shake side to side during the vibration , but the head rests on the front seats can be felt to move forward / backward .
I originally thought CB carrier wobbling but I set up a GoPro to film it and it does not appear to move oddly .
This has occured through many changes in my truck from stock / stock wheels + tires to lifted and larger tires
The common denominator seems to be the slight uphill load on the truck .
Is there any component that would vibrate in these conditions ?
FWIW , my driveshaft has been replaced under warranty for signs of cracking near the union at the CB .
Tires have been road force balanced , OEM Sport alloy wheels have been replaced for another warranty issue ( bubbling )
Any thoughts ?
Thanks in advance .