A couple days ago I posted saying I had a strange sound and vibration on my 99 tahoe and I thought it was the u-joints but the sound has returned. Actually it only does it when the truck is warmed up. It does it mostly when driving about 55 mph and will stop when you let off the gas or speed up, but its not continuous. It feels and sounds like driving on rumble strips. After reading some other posts it sounds like maybe its the torque converter failing. I just replaced the radiator the day this started and am wondering if maybe one of the oil lines got some junk in it or something. Will changing the transmission fluid and/or filter make any difference?