When's the last time you checked your timing? Perhaps it was retarded unintentionally. What kind of condition is your clutch in? If it is slipping this *could* cause you to not be chirping gears as often. As for the loss in oomph, recheck to see that you gapped your spark plugs to the proper specs. It's something like .044 --- might be off a couple, but it's close to this (see FSM, Chiltons, Haynes). Worth a shot.