Don't like the sound of that at all.
 

So last night a couple strange sounds happend while starting and driving my truck. After being at the orthodontist for about half an hour I went back out to my truck to head home... I started it up and it sounded like it was going to fire up just fine and then in mid-fire it made a bit of a clunkish sound and died. I figured I just hadn't turned the key long enough as it started all the way up on the second turn. But then, on the way home I was going up a pretty big hill at about 35-45mph and this strange clunking type sound occured. I believe I may have pulled off the throttle right before. (Second time its done that while driving up a hill) Since it's hard to fully describe a "clunk" while typing I'd compare it to the sound of a diesel starting up if that makes any sense. No lights came on and it quit after about 3 seconds. Has anyone experienced this kind of thing or sound? My truck is an '05 Lariat 4WD. I'd appreciate any ideas or knowledge you have on this sound. Thanks!

I also have experience that weird clunk sound/feel going up a hill here locally around work. Does it always happen on the same hill or on different hills. I just chaulked mine up as the hill around here at work having poor quality asphalt.

It's not on the same hill. They are similar hills in their length and steepness. I'm about 99% sure it's not from the smoothness on the road. The sound comes more from the engine area.

Mine did that before they did a reflash. The reflash is what they advised should take care of it.

On mine, it was at a low speed up hill. The second time it did it, I realized that the transmission shifted rapidly through the gears until it hit OD.. when it should have been downshifting if anything... which completely overloaded the motor and made all sorts of nasty engine sounds.

The second time, mine actually switched OD off all by itself.. which is what caused it to return to normal.

Hasn't happened since the reflash (also had a new transmission installed at the same time for the vibe problem)... but I haven't repeated the circumstances with it yet either.

Thanks for your input. I believe what you're describing is exactly what's going on with my truck. The funny thing is, is that I just had it reflashed about two weeks ago. I believe they did do the reflash as the acceleration problems I had previous to it are no longer a problem... Are there different flashes for differing problems?

I don't believe so. I think they just reflash to whatever the latest version is.

That's what I thought. Well hopefully it doesn't happen again. If it does I guess I'll just bring it in and see if they have another update.

I suspect a possible intermittent sticky injector......Mine did this one time, when cranking the engine made a SOLID clunk and stopped. Then I give it a second and when it cranked it was misfiring like a son of a bitch at idle and tons of raw fuel comming out of the tailpipe. The clunk was actually the engine hydrolocking from the excessive fuel being dumped in the cylinders. I don't know if this is your same problem but I wouldn't overlook it!