Trans lock up in & out

[Pencil craft]

HI I have a 1999 chevy 3500 w/ 6.5 turbo. when driving the lock up on the transmission torque converter will lock up under slight load at 47 mph but it unlocks on flat going or if I go down a small decline. it locks and unlocks 4-5 times a mile.
also it does not unlock when I tap the brake. One more thing above 45 mph the accelerator is delayed. if you are stepping on the pedal to speed up when you let off it takes a moment to quite accelerating Please help
Thanks
Vic

[DennisG01]

Are you letting off the throttle completely, or are you still keeping some throttle? Unlike a gasser, the TC will unlock when you let off the throttle - the rpm's won't go all the way to idle, but close. The "brake touch" will take it to idle. I'll let someone else the throttle problem, but I'll venture a guess at the throttle position sensor.

[DennisG01]

I did a quick search (search function above) for "Test APP" and found the thread below. I used the wrong term in my post above - it is the APP -- Which I think stands for Accelerator Pedal Position sensor. I'm sure you can find more.

http://www.thedieselpageforums.com/tdpforum/showthread.php?t=21839&highlight=TEST+APP

[Pencil craft]

It locks and unlocks when I am going a steady speed. even with the cruise on
If I am going up a sleight hill or keep accelerating just a little it will stay locked in. but on flat ground its in and out
Thanks
Vic

[Pencil craft]

Does any body know where to get the APP at a better price than the $485.00 at the Chevy dealer?
Vic

[DennisG01]

Does any body know where to get the APP at a better price than the $485.00 at the Chevy dealer?
Vic

gmpartsdirect.com

But I wouldn't go out and get it just yet. I'm decent at figuring things out, but there's a bunch of guys here (and a certain gal that I can think of;)) that are much better - if you can wait it out. Besides, it might be something like solenoids/tranny line pressure. I'd just hate to see you replace something that doesn't need to be replaced.

[DmaxMaverick]

Welcome aboard, PC!

If your APP is having issues, you will have a "Service Throttle Soon" lamp on the dash, as well as DTC's stored, and possibly the SES lamp. The APP is simple. It has 3 independent circuits, all 5 volts. Two at 0-5V and one at 5-0V (or the other way around). The 5V circuit will decrease voltage, and the 0V circuit will increase voltage, as the throttle is depressed. If you test it with a VOM, use an older style analog meter, instead of a digital. It will show the sweep more smoothly, while a digital will not show dips or spikes as clearly. The pedal motion should be smooth, off to full, without any rough or sticking transition, physically or electrically. If you have access to a Tech II or Snap-On scanner, you can read the values directly from the PCM, as it sees them. If you know someone with a Predator programmer (for the Duramax), I've had some success reading many 97+ engine parameters, including the APP, on nearly all GM vehicles.

I don't think you have an APP issue. It sounds more like a ground or wire/harness issue. Could also be the brake switch above the brake pedal. Lastly, the IP may need some attention.

[Pencil craft]

Any more help PLEASE
Vic

[Burning Oil]

Might be a simple as your brake light switch. If its at the point that alittle vibration from the pedal keeps activating it. Ajust it so it makes solid contact with the pedal.