2008 Chevrolet Silverado

Engine Performance problem
2008 Chevy Silverado V8 Four Wheel Drive Automatic 62000 miles

I'll try to keep this short.
A few weeks ago while traveling, my engine dropped a valve under warranty. A bunch of white smoke later (I assume a compromised combustion chamber) it was flatbedded to the nearest dealership. The dealership replaced the engine under the Powertrain Warranty - so far, so good. Since I live about 3 1/2 hours away from where the truck died, when it was complete I had to pick it up on a Friday night after hours. I got in it, drove 30 miles or so, and the check engine light came on - P0171 and P0174.
On Monday, I called the dealership (remember, 3 1/2 hours away) who informed me the problem was emissions related and NOT under warranty. I won't bore you with the details of arguing with " customer service" reps that one thing probably led to the other. But I'll get to where I am now.

I had the engine scanned at a local dealer, where I was told both the upstream O2 sensors were bad. To save a few dollars, I replaced them myself. Same Problem. I signed up for the Mitchell manual, and started through the diagnostics. Thus far, I've replaced not only the O2 sensors, but the MAF and MAP sensors as well. I still get the same codes. I was able to borrow an inexpensive scanner, and here's what the freeze frame is showing:
B1 - Closed Loop, using HO2S
B2 - Closed Loop, using HO2S
Calculated Load 11.76%
Coolant Temp 89 degrees C
ST Fuel Trim B1 6.23%
LT Fuel Trim B1 29.67%
ST Fuel Trim B2 10.14%
LT Fuel Trim B2 29.67%
MAP 41 KPa
Engine Speed 1077.50 RPM
Vehicle Speed 59 Km/hr
Ignition Timing29.50 BDTC
MAF 4.82 g/s
TPS 21.56%

I'm pretty much at a loss where to look next. Any help would be appreciated! I was supposed to leave on vacation today, so I have a pretty displeased wife!
June 28, 2010.

Lean fuel condition could be caused by one of the following below: 1. Vacuum leaks

2. EGR and PCV valve.

3. Low fuel pressure.

4. Dirty fuel injectors.

5. Mass Air Flow Sensor.

6. Oxygen Sensor.

Jun 29, 2010.