Cause of fire in trunk

Yesterday, when driving 95 Lss,3.8 home from work, the muffler got so hot it actually set the pad in the trunk on fire. Car has been experiencing the same sluggish running condition noted in many other threads (rough acceleration and poor performance) replaced the usual suspects (plugs, wires and fuel filter) but still runs rough. I thought it may have been starved for fuel (dirty filter), but now suspect it may have been getting too much fuel and the excess is somehow being exhausted into muffler where it burns and caused the fire in trunk. Any thoughts on this and suggestions would be aprecciated. THANKS

It could be the 02 sensor located on the exhaust it wouldnt hurt to replace it anyways you should replace them with every tune up anyways. Also the ecm computer may not fully correct itself until 40 miles of drive time.

I would suspect a faulty egr valve,I've seen some mufflers glow almost white hot from this problem and this would account for the performance you have had.