As mentioned a couple of times now, you need to look at the exhaust velocity. You will probably find that 3" the whole way will drone badly. If you go dump,cat and front section of pipe at 3", then reduce down to 2.5" just before the diff, and mandrel bend over, with a free flowing 2.5" fibreglass packed muffler, that would produce a nice bark, flow quite freely (gas contracts as it cools, and thus less cross sectional area is required to maintain velocity at the back) and would not restrict your flow.