GM Repair Problems? Ask GM Repair Expert Now.
Hi there, I am Cam. Along with this clunk, is the check engine light on?
Ok, those will cause shifting issues. The fuel system on yours does not have an external filter. If the integral filter is plugged it reduces the actual power the engine can put out, you want to go faster, it does not respond so what is your natural reaction? Push the fuel. Since the shifting is controlled buy a combination of 3 things, engine speed, vehicle speed and throttle position. Normally you push the throttle down all the way you want more speed so it down shifts and goes to high RPMs. IF there is not enough fuel to fully make the power at that RPM, the engine will simply run at that RPM but make little power and when you do not feel it moving or accelerating, it gives the feeling of slipping. So a plugged filter can do this, or be the cause of the larger issue. A plugged filter will eventually damage the fuel pump due to the strain of trying to push the fuel past the restriction and that in turn makes the pump weak. So to accurately measure this we need to see what the fuel pressure is doing when it is trying to go faster. So when driving. IF that is fine then the next option is the exhaust. If the filter was plugged it can cause a lean condition, which is no power and that can damage the catalytic converter which will cause the engine to plug up in a way, meaning it cannot push the exhaust out and that will also cause a lack of power. The test for that is a back pressure test done by taking the front oxygen sensor out and either driving it or testing back pressure. Anything more than 1 psi at all RPMS is too much.
The bands are not adjustable so it's not that. It might be the torque converter clutch. If you take the lower cooler line off at the transmission, is there debris in there? These are know for that clutch coming apart and the clunk/shifting would be the result.