There are times that the traffic is not too bad - like Saturday early afternoon. The big problem is TBIT mid afternoon and evening with all the international departures.

People are suggesting you walk downstairs cutting through the roads. My suggestion was you walk upstairs through the horseshoe. T3 is almost at TBIT and you avoid the traffic lights and sidwalk/road junction ramps which can be hard to maneuver with a heavy load.

I would think if the porters would take the bags to the garages with people, another terminal is not a problem. You would think it comes down to a good tip since it will probably take them 3x the time.