The Brits had their own doctrine and their own thinking which led them down this path. The fact remains, as I know it, that reactions from men in the field was indicating no urgent need to upgun the M4. We might have had an interest in putting 90mm's in the field in '43 but not in an M4. No need to make it sound so problematic. The US was not alone in squabbling over armor doctrine or design. Panzer Leader is a good insight into how messed up this can be. Best remember that getting the 90mm in to a tank was pretty much a waste of time.