"resistance" while starting to move forward

[SkylineNXS]

Hi guys,

I have a 2000 gmc sierra 5.3 4wd with around 107k. Starting around last winter, there is what seems to be a resistance or sticking when i start to move forward from a stand still. It seems like you have to give it a little more gas before it starts to move, then after a couple seconds that resistance goes away and it moves along fine. This originally occurred rarely, but now its making itself more common.

Im wondering if this has to do with transmission, transfer case, or rear end? I bought this truck from my dad and it has never had a trans or rear end flush or anything like that. Any ideas?

Thanks.

[clinebarger]

Check engine light?

[Old Money]

check u-joints. my 05 gmc was doing that at 64000 miles and then it started to squeak also. factory no grease zerks. put new ones with zerks in them and it all but jumped forward at idle. old money.

[truckdude239]

sounds like it might still be in 4x4

[SkylineNXS]

No engine light on, i pretty sure its not in 4 wheel as even if its in 4 wheel auto, i can feel it through the floor o so subtly. I pretty sure its not in 4 wheel, but cant exactly be sure. I will look at u joints as well, thank you for the recommendation.

Brad

[Boog]

Brad I have the same occurance with my 2000 GMC. I've had the truck for almost 3 yrs and it's done this maybe 5 times. When it happens it feels like the brakes are holding it back but I believe it's more like the trans is not downshifting to 1st gear like it should. Sort of like it's starting off in 2nd or it's in 2 gears at once. What I found to work is as soon as I feel it doing this I let off the gas for a second and push it again. When I do this it restarts in 1st gear as it should. No noises or check engine lights accompany this weird start. It only happens when taking off from a stop. Always was fully warmed up. Mine only has 150,000 miles on it.
I've hoped one of our tranny tech members might have some experience with this.

[ncl5047]

if you have 107k on it a trans flush wouldnt hurt at all and it may just take care of that resistance.

[truckdude239]

at 107k id drop the pan and change the filter and fluid

[Boog]

Someone mentioned it might be a worn tps. Since the computer uses tps to select proper gear selection for load/throttle requirements it does sound plausible. I have reason to believe my tps is original and on some occasions it seems like it should have downshifted on a passing maneuver requiring a good bit more accelerator but didn't.
I've had the truck going on 3 yrs and have only replaced the iac and fpr so far.

[clinebarger]

Originally Posted by Boog

Someone mentioned it might be a worn tps. Since the computer uses tps to select proper gear selection for load/throttle requirements it does sound plausible. I have reason to believe my tps is original and on some occasions it seems like it should have downshifted on a passing maneuver requiring a good bit more accelerator but didn't.
I've had the truck going on 3 yrs and have only replaced the iac and fpr so far.

A "PCM reflash" at the dealer might cure this, Ive had this fix alot of 99-00 trucks with shifting problems.

An intermittent VSS signal can cause the PCM to command second gear.

Debris on top of the spacer plate or in the valve body or a leaking shift solenoid can cause a 4L60E to start in a gear higher than first.

[SkylineNXS]

Thank for all of the info guys. I think the first thing i'll do is flush and make sure everything's clean, then if it persists I will take a look at the tps or pcm. Thanks again.

Brad

[SkylineNXS]

Hi gents,

So I took it to a shop after doing a trans flush with no luck. After reviewing it, they claimed a bad fuel pump. However, after looking into it, it seems most bad pumps show themselves on start up in certain conditions. I have none of these issues, so I am a bit skeptical. I did change the fuel filter as that seemed like a good choice, since the engine would bog down at speed with load. However, this filter change did nothing.

I took it out after the change and once again experienced the issue. To try and rule out fuel pump, once the issue started to occur, I would shift to neutral and rev the engine up to 4-5k. This to me would mean the fuel pump is retaining pressure at speed and the engine is able to run at high rpm, however, this is unloaded.

I have a slightly better issue description. It will time to time happen at a stop light, but most often at higher speed. If i am on the highway cruising at 70, and try and push it higher, rpms will seem to "stick" at 3k or so and not accelerate the vehicle. Sometimes, after fluttering the gas a bit, I can get it to accel slightly, but other times, it will sort of "cut out" and no amount of fluttering will get any power back, and I will have to coast to the side of the highway and let it sit for a while, fluttering away at the pedal, until finally it will find some power and move.

It still seems to me like a trans issue as it will hard shift every once and a while and get up to the next gear, or down to the one i want, but it is certainly resilient to do so. However, the cut out issue also makes me suspect the fuel pump, or maybe the fuel sock is just jammed with debris. I am trying to find low cost solutions as I have little to money money for a major repair, but I am running out of ideas.

Other items, fuel pressure regulator is working fine, and I plan on getting a fuel rail pressure tester soon so I can rule out fuel pump if possible.

Any other ideas would be helpful, however I think I am running out of low cost solutions. Thanks guys...

Brad