'08 V6 with 70K miles. Last weekend I installed lift/tires, and changed the oil - although I can't imagine either of those having anything to do with this new problem.

After doing the above, I now have a strange intermittent significant loss of power. From a stop when accelerating, the truck will barely get out of its own way. While at speed and hitting the pedal to downshift, it struggles and barely gains speed. In neutral or park, flooring it will result in rpm's barely above 3,000.

Here's the strange part - it is intermittent. It will exhibit these symptoms for a while, but two stop lights later it will scoot away and run fine. The engine will freely rev in neutral/park, and it runs great. Few minutes later, it runs really weird again. "Indicated" mpg on the display has gone from a typical 20-22 down to 15-16.

Additional information:

Plugs changed three months ago
No misfires/sputtering/rough idling at all
Checked MAF and TPS connections - they are tight
MAF sensor and throttle body cleaned about a week ago
No lights on the dash
Haven't fooled with anything under hood to cause a vacuum leak

Any ideas? It would seem to be electrical in nature due to the coming/going of the symptoms, but that's a guess. Is there anything obvious that I am missing? This is really a mystery and I need to figure it out.

What size tires did you put on? Taller heavier tires take a lot more power to turn and will make a vehicle feel sluggish.

265/70/17's. But tire size would not cause an intermittent problem.

Actually you may have forgot to connect the vacuum hose at the back of the air intake box since you had that off to clean the TB.

Good call, Fish, but I know I connected it because I recall it being hard to see back there. But I will definitely check that out again tonight. Thanks.

Just took it to lunch and it acted perfectly fine. Really weird.

Yeah intermittent problems are always the worst. Good Luck with your hunt!

hmm I suspect an intake problem, either an air leak, or loose vacuum hose or a faulty MAF sensor.

what did you clean it with?

Do you happen to have an oiled air filter? did you re oil it when you put your intake back together?

Red, I cleaned the MAF with brake cleaner then blew it out with compressed air. I did not re-oil the K&N that's in there, as it is only a few months old. Faulty MAF or TPS are at the top of my list right now, but nothing's blinking on the dash. I assume a faulty sensor would cause something to blink, correct?

I've got a bluetooth OBD gadget coming in the mail so I can scan with the Torque app for fault codes.

I'll spray some starting fluid around to see if there's a vacuum leak I'm not seeing/hearing.

It is possible that you damaged the MAF using brake cleaner and compressed air, from what I've read the wires in there are pretty delicate and its recommended to use CRC MAF sensor cleaner and let it evaporate on its own.

You'd think you'd get a code from that but maybe not?

Well, the truck behaved fine the whole way home yesterday, and on the way to work today. Last night I sprayed the engine down looking for vacuum leaks - none. No sensor connectors out of place, etc. It's a real mystery, but I hope it is gone. Thanks for the tips, guys.

Well, after six months the problem is back again. Same exact symptoms - huge loss in power, MPG goes down the drain, etc. Next trip in the truck, it's gone. Two trips later, it's back. WTF would cause this issue? I'm monitoring likely parameters in Torque but see nothing that stands out. Do these trucks experience sticky throttle blades in the TB?

I don't see anything unusual in the ignition advance, STFT's, A/F, relative throttle position, etc. No vacuum leaks found either. No codes or faults in Torque. Something really strange is going on...

I'd be mighty curious if it's not a clogged or partially clogged cat. Thoughts?

i have similar problem, and i have p0430, and p0420 codes. so it might be true

Your upstream O2 sensors may be acting up. Or you Mass Airflow sensor may have finally sh*t the bed.

The upstream O2s are a bit tricky to get out but with an O2 sensor socket and a flex head 3/8's ratchet it's not too bad. I recommend doing the passenger side from above in the engine bay. The driver's side is easiest through the wheel well and beneath the vehicle.

Check your fuel trims.

op, did you ever resolve the problem?