Do you have the air suspension on your HC? I don't totally love the ride on my At4 6.2 w/air - it can be a little harsh over bumps. I held out for the MRC + Air combo thinking that would give the best ride. Many of the reviews i read raved about it 'floating down the road' and i certainly can't agree with that after a few months of ownership. The 6.2l weighs a couple hundred pounds more than the 5.3l IIRC - so the 5.3l front end may feel a little lighter but I don't know why the dealer would connect ride noise to your 6.2l. There shouldnt be any rumbling .... there is a bulletin about noise coming from the wheel liners on '21's. I'll try to find and post that..
Actually Like2detail had posted it recently in another thread :
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