I apologize for posting this here. I know there are many knowledge transmission experts here who can give me some advice. Having problems with a 2008 Colorado 4L60e 175K miles. Transmission shifts perfectly firm, quick, no slipping or delays. I think the torque converter is having trouble staying locked (shuddering). When the converter locks the rpms drop to 1500, moving about 45-50 mph and a demand to accelerate. For a brief period there will be a metal rattle sound or maybe rumble sound heard and felt mildly to medium from the floorboard. Don't feel like it is slipping/grabbing. If it is going faster say 55 mph it will not happen. Only when the rpms are very low (as low as they can be for the trans to lock up the converter) and the gas is pushed lightly causing the engine to be in a lugging situation for acceleration. If the trans downshifts or unlocks it will not happen. It also, goes away after the truck accelerates about 5 to 10 mph faster. Hooked up a scanner and there are no codes or misfires. Checked the fluid level and it is full. If anyone can help me diagnose this or get me in the right direction it is greatly appreciated. Even if you might know a a site where knowledgeable 4l60e techs are would be a great help. Sorry it is not TR related. Thank you.