The Toyota engine needs a muffler which will give a little back pressure at low rpm, but release that backpressure at high rpm. A perforated core 'flow through' style muffler does that.
As the exhaust pulse travels down the tubing it enters the muffler. When it hits the perforations it expands into the canister where the sound is absorbed. As the exhaust slows down to enter the canister it 'puts the brakes on'. This creates backpressure.
When you really step on it, the exhaust remains at a steady pressure. When the pressure in the canister is the same as the pressure in the exhaust tubing, you have a flow through muffler.
The most important thing to remember in a stock system where you're only changing the muffler is to keep the tubing and perf. core the as close to the same diameter as stock as possible. Slightly larger is better than slightly smaller.
The next thing that to consider is canister diameter and length. A huge Magnaflow RV muff will be waaaay oversized for a small displacement V8. On the other hand a 4in race muff won't have enough back pressure for long enough.
The best size muff generally is stock diameter inner core, 5in. diameter 12in. long canister. Borla, and Magnaflow make excellent mufflers. Simply cut out your resonator, if you have one, and your muffler. Replace with appropriate tubing and muffler and you just gained more tq. hp. throttle response, and fuel economy. Another option for High Performance Mufflers is
BAMufflers.com