2000 LMTD, 3.4, Auto, 4x4.

Yesterday I'm headed back from a 3 day trip with the family and the truck starts doing something funny. I first noticed it when I started climbing a hill on the interstate, truck downshifts from OD to D as it always does, but instead of revving up and powering up the hill, it falls on its face. I kicked the cruise off, get back onto the throttle and it starts climbing as usual. Weird. I chalk it up to maybe the cruise did something funny.

Couple minutes later, another hill, same thing. This time though, when I get back on the gas, it climbs right up to 3400 RPM and cuts power, no shuttering or anything like that, just cuts power.

The interesting thing is, I can hold it to the floor, it just keeps decelerating, until I let completely off the pedal and get back into it then it will climb right back up to 3400RPM exactly and cut power again. If I let half off the pedal and get back into it nothing, I have to let completely off the pedal, like its reseting or something.

I did get it to do it in 2nd gear too, except it would run up to 3800RPM and cut power, got it to do it about 3 times (always 3800RPM Cut out), but didn't do it every time. Sometimes it would run right up to redline.

Never got it to do it in first or neutral.

No CE light, ran the codes and had a PENDING PO171, lean condition. Pulled the MAF and it was covered so I cleaned it and put it back in. I've had this code before though and it never put the truck into a limp mode.

It's not missing, its like someone is throwing a switch, its that fast and absolutely wont make power again until i fully get off the gas and back in it, then its normal right up until that particular RPM.

Seems sensor related to me but not sure which one, any thoughts?

I think you are on the right track. It sounds like either a sensor or the ECU was not supplying enough fuel to make power. If you have access to a scan gauge or cheapo bluetooth reader + Torque app you can view your fuel trims to see if it's trying to dump or pull fuel.

You could also have a vacuum leak causing the P0171. Have you done any work on the engine lately and possibly left a hose off?

I changed the oil last week, thats the only thing that has been done recently, I'll check again and see if I knocked anything loose. I do run a scan gauge, I'll look up those fuel trim numbers again and see what it does.

I've experienced a similar symptom, RPM drop while driving often while using CC

I suspected fuel originally but then I focused on electrical/sensors. I went around and unplugged and replugged all the sensor harness plugs as well as the ignitor harness connector and my truck has not stumbled once since.

That would definitely be an easy fix! Thanks.

Figured out the problem... I installed one of those spin type pre-cleaners on top of my 167 snorkel last week. While driving to work the morning after I typed this up, I ran it up to see if it would still do it, it did. With the window down I noticed, when it lost power, you could hear an almost "air sucking through 2 pieces of rubber" sound coming from the snorkel. That got me thinking about the issues the Supercharger guys have had with the rubber connector that the 167 snorkel uses, collapsing under boost. So I pulled the prefilter off and the issue went away. I ran it all this week like that with no problems. Put it on today to verify and the problem immediately came back, take it off, problem gone.

I guess the thing just can't flow enough air for the engine at higher RPM's under load (3400RPM-ish). Its pulling enough suction to collapse that rubber connector I believe. I don't have a camera that will fit up in there to verify but I'd put money on the issue. This is the unit I bought:
https://www.amazon.com/Spec-D-Tuning...rkel+prefilter

The pending code went away the first drive after cleaning the MAF sensor.

Just for future FYI, and thanks for the responses.

Glad you got it figured out

I ask u before 2001 in limp mode now I replaced ads/THC/vsc and ecu no cel no pending I’ve put100 miles trying to all green but cat and Evap never change from red should I get better scanner or is there a scanner than can reset everything