I have a 2006 Buick Lucerne cxl and my reduced speed message came on and now my car only goes 20 mph in drive and 40mph in drive 4 can someone please help

Reduced speed is usually set by a code...we need that code........usual problem is the TAC system, throttle actuator control......what this is, is electronic throttle control, which replaces the old cable system.....if one of the two throttle position sensors gives the wrong data, or one of the circuits is open, the code is set and you have reduced power......

I have said this before, have seen a lot of parts replaced, when the problem was the wire harness to the throttle body......sometimes a wire can be broken inside the insulation or there is a bad connection from the wire to one of the harness pins......