while driving car slowed down and would not accelerate past 5 to10 mph

I was driving on highway car started slowing down and would not accelerate even though I pushed the gas pedal to the floor. The engine stayed on and the car will turn on again after I shut it off it just wont move. The car did not over heat, leak or make noise and it stayed on. Had to pull over to emergency lane and slowly get off exit to get towed to mechanics.
He said alternator is not charging, but it did not have problems starting. this car has had so many problems before that I fixed in 1 years time:
head gasket, cam shaft, time sensor, oxygen sensor, fuel system, catalytic converter, brakes, cables, spark plugs, clean engine, fire in the cables, oil changes and new battery. please help
I think it’s the catalytic converter again, and sensors, or fuel systems,
Do you know what it could be before I get ripped off by this mechanic
Thank you for your time
Jenny