Was looking for some help on my problem. When driving Highway with overdrive on, and sometimes with it off, if I am driving at around 1500-2500 rpm and lightly hit the gas, I here a grinding noise behind me(close to what rumble strips on the side of the road sound like). If I give it a lot of gas, it goes away and my speed increases. If I just drive and give it gas, it shifts fine. Any ideas? I was thinking torque converter maybe but that is probably way off.

 

Take a look at the transmission mount and the torque arm bushing.