904 swap 65 valiant

Unless yoru willing to switch the pushbotton shifter to a lever shift you don't have any option but to stay with a 65 or earlier 904. As far as their being a better trans., the 904 is a great trans. Yours is just probably worn out cause it's nearly 50 yrs. old. Not much else out there better unless you get into a O.D. trans. which will take a lot of work to install and cost quite a bit.