I have a 2003 5.3L (T) silverado that is throwing codes P0171 and P0174. Some information:
125,000 miles
Replaced MAF sensor 5 months ago because it was throwing that code, ran fine after that.
Tried cleaning Throttle Body 2 months ago and must have ruined the sensor because it went into REDUCED ENGINE POWER mode. Had to have a new Throttle Body installed. After that was installed I could tell it idled just a little higher, but nothing that caused concern. When I would start it it would rev much higher for about a split second and then return to normal. Ran fine.
Replaced Fuel filter and spark plugs and wires 500 miles ago(AC Delco wires and AC Delco Iridium Plugs) Ran Fine.
Now the CEL is back on again. I pull codes P0171 and P0174.
I exchanged the MAF sensor again because it was under warranty and that didn't change anything.
Here is the data I pulled with my Actron CP9575 with the vehicle key in the on position (vehicle not running). The vehicle had been sitting outside for 2 days when I did this test.
MIL Status ON
ABSLT TPS(%) 18.4
ENG SPPED (RPM) 0
CALC LOAD (%) 0.0
MAF (LB/M) 0.00
MAPC ("HG) 29.2
COOLANT (F) 50
IAT (F) 59
IGN ADV 0.0
ST FTRM1(%) 0.0
LT FTRM1 (%) 25.0
ST FTRM2 (%) 0.0
VEH SPEED (MPH) 0
FUEL SYS1 Open
FUEL SYS2 Open
O2S11(v) 0.445
ST FTRM11 (%) 0.0
02S12(v) 0.445
02S21(v) 0.445
ST FTRM21 (%) 0.0
02S22(v) 0.450
02S22 (v) 0.450
PTO Status EISE
OBD2 STAT CA^

Any help? Should I run a different test??

Thanks!