1992 Nissan Sentra Problems after new exhaust installed

We just had our entire exhaust system replaced. Now the car isn't driven much, but on a short trip, my wife said the car started "bucking" at stops and it smelled like extreme hot when she returned home, but no change in the temperature gauge. Now I believe the power steering is low and I will fill that, and she also ran the gas tank really far down and it has been extremely cold and windy. The power steering fluid is "hot" smelling. Are the problems related? Is it possible they cut or screwed something up when doing the exhaust? Is it a case of maybe moisture in the lines due to her running it low and low steering fluid? Why would it get so incredibly hot smelling? Thanks in advance.