2002 dodge durango exhaust help?

it is because the catalytic converter pushes a lot of the exhaust back through the engine for reburning...disconnect your egr valves vacuum line and cover the hole....what is happening is without the muffler there is no back pressure in your exhaust and it is essentially "Coughing". without a muffler you will not get that back pressure and all the gas is trying to escape at once. 2 1/4 should be plenty enough for a 4.7 but i would have just put fibergl inside your muffler then welded it back together......makes a home made Gl Pack while cutting down on the escape of exhaust.....Or buy gl packs.....itll sound like a pissed off harley