2004 Chevy Avalanche the transmission feels heavy

it's best to have a trans pro check this as it may be ann elctrical problem inside the trans. It could also be that a clutch pack is going bad or a seal has worn out. make sure your fluid is full. The trans pro can scan the trans to see if there are any problems with shift valves, etc. YOu could have two clutches applied at the same time that aren't supposed to be.