Codes 171 174 2002 gmc sierra 5.3

Check your fuel pressure, early 2000 rams are notorious for fuel pump issues. They start but run rough or lack power.
Were the lean codes for both banks 1 and 2? (P0171 and P0174)

with out a doutb its the o2 sensors. replace them and all codes will go away.

Code 53 is for a problem with the heater in the O2 sensor for bank one sensor one. It could be something in the wiring or you could have a defective sensor.

COULD BE A WEAK FUEL PUMP

You never replace anything, on a Wishing,Hoping,Pushing,Poking,diagnostic approach

You learn the vehicles Systems,Test,then Replace,if you have a failed component.

Work on the Misfire Issues.
Then you lean O2 Codes will go away.

Not a the plugs.

Think lean---Vacuum leaks,EGR Valve leak,EVAP System leaks,anything with a hose that lets air into the intake system.
Exhaust System leaks,near sensors

Bad fuel, bad air filter,PVC valve, EGR valve

More likely it's the intake manifold gasket leaking. They can become flat and **** air in passed the gasket, causing a lean condiiton.

Yes bad o2 sensor,check for vacuum leaks also.do you cross your plug wires?

171 is a lean bank one check for vacuum leak at the intake manifold

Nic, If the carburetor was dumping gas, remove the engine oil dip stick and see if it smells like gasoline. If it does you will need to change the oil.
Second, go back over your spark plug wires and verify they are on the correct spark plug. Start with the #1 plug wire, the firing order is 1,8,4.3.6.5.7.2...
Let me know how it turns out and we can go from there.
Good luck.