Help! Auto Transmission won't stay in lockup
 

Looking for some advice.

I've got a 98 Dodge Ram 2500 4x4 Cummins with an automatic transmission. I've had it for 2 months now. I bought it from a fleet that my cousin and uncle maintain as mechanics. Needless to say it's been pampered and upgraded throughout its life. It's got a rebuilt transmission by an awesome shop just over a year ago.

The issue has been recurring and was thought to had been solved but reared its head again a month ago. The truck can't decide if it wants to be in lockup or not. It has (not sure what it's called) an add on system that is supposed to hold the trans in lockup. At 48 mph under normal acceleration you'll hear a little air release and the gas pedal drops a bit. That's when its working right. When it's not, it will rapid fire that air release and jump in and out of lockup.

Here's some more information that may help. It's interminant. Will go days, even weeks without doing it. The guy who built the transmission said that it is alternator related. I've put two brand new alternators in it. After both installs the issue left for two weeks before returning. When the issue is happening the gas pedal is VERY light, making it very difficult to hold speed. It does it when cruise control is on.

On one hand I hope none of you have had this problem because it's very annoying. On the other hand, I'm hoping you have so you can help me out.

Thanks!

Nathan

RE: Help! Auto Transmission won't stay in lockup
 

There have been several posts on surging cruise control. Run a search in the 2nd gen forum on that and see if it answers your questions. You might want to post in the Cummins Turbo diesel forum as well and see if any of those guys know, as they'll know yourtruck inside out better than some of us gas guys, if that matters to your particular problem.

RE: Help! Auto Transmission won't stay in lockup
 

I have the same truck and have had the same problem 3 times and it's starting to do it again. The dealer warranties it for 12 mos and it always goes bad in 13. Each time, he has replaced the throttle position sensor (TPS) at a cost of $350 for the part and $700 for labor. Others on this forum have said that the TPS is available from NAPA for $55 and is easy to replace. So that's what I'm going to do in the next week or so.

RE: Help! Auto Transmission won't stay in lockup
 

Thanks! I'll post on there as well. One clarification, I typed the cruise thing in a confusing way. I should have said it does it with cruise on as well. The issue is an always thing, not just with cruise on.
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RE: Help! Auto Transmission won't stay in lockup
 

$700 for labor? Wow. Maybe it's a lot harder on the diesel. On my 360 I had a problem about like you are describing and it was the tps. It was like $50 from Napa I think and took like 2 minutes to install. Maybe it's a lot harder on the diesel idk.