Harley Davidson Softail Deuce Screamin Eagle. 6 speed transmission. New oil and diamond tip plugs and wires. The speedometer quit working and at the same time it started trying to die on me when i slow down, the exhaust sounds muffled(or flooded) when i am down shifting through the gears. but it has plenty of power otherwise. and the flooding dieing issue only happens when it warms up.

 

It may be your new plugs and wires. Just exactly which brand(s) did you switch over to? The ECU may be getting the wrong signals as to when to fire the plugs.