howdy! i have read on here about people have a "shuttering" problem at different speeds. so here is my problem:

i don't think i would necessarily call mine a "shutter." I have an 08 f150 xlt. it has right at 40k miles and has been taken well care of. when i am driving and start to go up a hill and the tranny downshifts, i get a noise/feel as if i am going over a rumble strip from the rear end for about a split second. it only happens when it downshifts. i have only been able to "make" it do it a few times. it doesn't do it all the time, just when i am heading up a steep incline. any suggestions?