Got a code on 2004 trailblazer (P0172). what is the main problem for this code?

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Well i bought this truck for my son and from the first day we had it was problems. First it was a code for air injection pump, changed it with air solenoid valve. Next got a code for Temp. too low, changed new temp-stat. Now, code of P0172. the truck is smelling like the fuel is too rich and it also lack power when accelerating. The internet says it oxygen sensor or clogged catalytic converter. Please help. P.S. also changed air filter and fuel filter. If i dont fix this truck soon my wife will punish me, she's on my tail bout this lemon i bought cause we always bought Toyotas.