904 differences

I haven't gotten to your mod yet but it is on the list of possibilities , I'm really not looking for big hit shifts , I just want to be sure it's shifting good and not slipping , It's got a 323 rear end and the 245/60/14s making it a great highway cruiser with plenty of power to pass , all that power and torque means it pulls up the side of the Rockies at like 70 mph the way most cars cruise on the flat lands with no effort at all maybe 2800 rpm or so that gives me pretty darn good mileage for a motor this big . is it possible to back flush the whole works if there is a little crud in the governer or the servo ?