A904 Woes.. not working right..

I have a 72 A904 behind a 318 in my daily driver.
It was recently rebuilt and has been driving well with nothing out of the ordinary. Until yesterday my son and I were curzing and running errands and left a bit harder at a light than normal, and instead of a burn out we got slippage so I let off and took it easy home. Once home I ran through the gears and then test the tran a bit, then holding the brake I gave it the gas and the tire chirped a bit. But now it slips and shudders bad in first under any throttle. Still runs and drives but make odd noises under load once up to speed.. At a loss and looking for help.
Thanks