2005 Suburban LF Front SIR Sensor is bad. According to the

http://engine-codes.com/p1125_chevrolet.html
According to that website above, its your Accelerator Position Pedal Sensor. If you have already replaced it check your wiring harness.
Here is a website that for your wiring diagram for your 2005 Chevy Suburban.

Sounds like the Knock sensor bolt has been over torqued.

usually the sensors (2) are good but the harness goes bad and there is corrosion at the knock sensor connection. The intake manifold need to be removed and the harness replaced. KNOCK SENSOR 2 IS THE REAR.

The ABS works according to what the speed sensor tells it. The sensor may be bad or it senses a broken tooth on the tone wheel (the sensor reads these teeth on the tone wheel, found in the hub).
You will still have Brakes, but not the ABS. You can switch the sensors from the good side to the bad to see if it is in fact the sensor itself. Good luck!

check the resistor i think it's a 7 way connector located by the blower motor i have had were the connector has melted to the resistor if this is the case you will need to replace both resistor and connector
the connector is available at a GM dealer or a AC DELCO parts dealer not sure about aftermarket
hope this helps

The Reduce Engine Power problem on my 03 Suburban went away when I had to replace the fuel mixing sensor. I damaged the sensor by topping off with E85 (ethanol) by mistake late at night. The vehicle just would not turn on in the morning. The vehicle had to be towed to the dealer. I was in Carlsbad NM about 800 miles from home. I had no choice but to pay $1,100 to get it fixed. At the same time the Reduce Engine Power problem went away. And thanks to God it has not come back for nine 9 months now.

replace the speed sensor

i would check your alternator if it just lost power while you were driving

Have an alignment done and request that a couple of degrees positive caster be added into adjustment (past specifications) Generally this will either cure or lessen wandering at high speed. Doing this will not harm performance in any way.

The sensors do activate on impact. All you have to do to disable the system is disconnect the battery and replace the sensor. I do not think the system has to be reset. I am not 100% sure on reset. I would ask on star if the system pinpointed which one. I believe there are more then one on the front and back. The sensor is mounted with screws and electrical connector. Very easy fix.

Good Luck