2008 Yukon XL Denali 6.2l No Mods

Drove through a huge rainstorm on the highway, check engine light comes on, read codes for knock sensors on both banks, symptoms are low power until 2k rpm is met, then runs like a dream, replace knock sensors on both banks, opened ECU connectors checked for water corrosion, was a small amount of corrosion, cleaned it and used di-electric grease, reconnect connectors, take the truck for a test drive, first 4 minutes it runs great through all RPM ranges, suddenly the same symptom returns, low power at low RPM, no check engine light. Any ideas?

On a side note, I was attempting to climb my hill to the house, would barely move up the incline, switched to manual mode, it was in 3rd gear which i thought was odd, shouldn't the tranny drop a gear if under load and getting a lot of peddle? So I manually placed the tranny into 1st gear, it jumped with plenty of power, then put it in 2nd gear, climbed the hill no problem......

I appreciate any and all help. Thank you. Jon

Is it starting in second or third gear when it is having this low power symptom?

Not sure. when I moved the shifter to manual, it was in 3rd gear at around 3mph. I can check in the morning and report back. Is it common for the yukon to start out in 2nd or 3rd gear? is that a problem?

Since we barely know each other and are on opposite sides of the internet, I need to confirm that you are saying that it was indicating that it had chosen to operate in 3rd gear at 3MPH or that it was showing that "3" was currently selected while in manual mode.

No.

3rd gear at 3MPH is a problem if it is actually engaged in 3rd gear at 3MPH.

I will do some testing today and get back to you with results.

Used my scan tool to do some tests.
Fuel trims are normal, O2 sensor Voltage acts normally.
When the computer commands a certain gear, the transmission immediately shifts to that gear.
truck starts out in 1st gear each time. shift solenoids are ON. 0.25 seconds to shift.
spark is 18 degrees. no retard from knock sensor, never.
vehicle speed sensors alive and working.
No misfires. MAF sensor numbers are normal.
Today I got another knock sensor low input code (is has two new sensors) so maybe there is a wiring short or corrosion in a connector?
Also the electric cooling fan sometimes comes on before the truck is up to normal operating temperature.

All good news!

Maybe, or a bad wire. We might be able to tell more if we saw the code.

This might be because the air conditioning or defroster is turned on.

P0332 Knock Sensor 2 Circ LO Input Bank 2

I bought some contact cleaner I am going to unplug every connector in the engine compartment and clean out, dry it out, remove corrosion, apply dielectric grease, see if that might remedy the issue...could be water hanging around somewhere?

Sounds like a good idea.

Some people go crazy with the dielectric grease. Personally, I use it around the connector seal and sometimes in the back end of the connectors where the wire comes in.