I'm new here.. I did a search and couldn't find my answer..

I have a '99 6.5TD Suburban with the 4L80E tranny. It only happens on long trips or if I'm towing.. Long trip, climbing a hill, tranny in D.. Doing around 50mph and the truck goes into safe mode.. basically down shifts and raises the rpms. I have to stop, count to 20 and restart to reset.

Same problem but more frequent when towing.
I have just over 150K on this original tranny. I plan to replace it with a CERT unit from GM BUT wondering if it could be anything else besides the tranny? Could a chip on the main computer be causing this problem or is it more likely something in the tranny?
We hooked up a recording unit where I push the button when this happens and it records all the sensors.. There was nothing conclusive.. Dealer said they could change the torque converter which was the most obvious problem however they couldn't guarantee that's the problem. That would be a $2,000 guess.. $2,675 and I get a whole new unit.. BUT if it could be something else I want to make sure we check that first..

Any thoughts?

Thanks!

There have been a lot of guys fix problems by checking and tightening all the grounds. And I thought I saw a post in here a week or so ago about something with the trans. and a ground inside it or something. If there are no codes I would check connections. Because I am pretty sure if they are slipping they set a code.

There was an 1870 code which I was told says tranny slip.. Could anything in the main computer think that the tranny was slipping when it wasn't?

Looks like you have the same yr truck that I have.. just a bigger rear. Where did you mount the boost, pyro and trans temp gauges? I'm still running a stock truck. Wondering if it's time for some upgrades.. What mod did you do that you feel you got the most out of your truck?

Thanks for the help!

From what I've been told no. If it stores an 1870 it has an issue. My buddy that works for GMC told me they kind of have a band-aid is a 1-2 shift soleniod and valve body upgrade. But he said all that does is raise line pressure and only helps out for a short while. I'll get some pics. of my gauge install tonight and put them on here. I think the best was the boost controller. It only cost $90 and once I put it in I noticed instead of the boost rising to 10 and just dropping off, it would stay at 10. I actually had to turn the controller down because it was boosting to high. But like when I would tow and you would get into the gas the boost would peak at like 10 psi and then withing 3 seconds it would fall off to like 4 psi. The boost controller would keep it at 12psi.

I'm guessing I would need to add at least a pyro gague with the boost controler? Did you do the installs yourself? How hard? Wish I had a buddy that worked for GMC.. :)

You should add a boost gauge if you get the boost controller. On my 99 I was hitting 19psi of boost towing uphill. And that was after I turned it down. I had to keep letting out of the throttle because the boost was going to high. Kennedy says that on his site to make sure you have a boost gauge before install. Yeah I did it myself. But I was to chicken to drill and tap a hole in my manifold for pre-turbo temps. The kit came with a weld on fitting so I took it to an exhaust shop and they put the hole and welded it to my downpipe. He charged me $20 to do it. And then I got what is called an "add a fuse" and plugged it into my existing light fuse and that way even the new gauges dim with the light switch. I go get some pics and post them. I didn't have a digital camera when I did the install to do it step by step. My truck already had the cat. removed when I bought it. But I ended up doing the whole exhaust anyway. I really didn't notice any difference in power. The stock downpipe looks pretty restrictive, but I don't think I noticed a difference. I have a friend that just bought a 96 powerstroke and my downpipe had a lot more flow that his does. I guess all of the manufactures restrict them alot.

Thanks for the pictures. I agree, I would have to add gauges before adding any other mods to the truck. I don't know what I want to do. The truck is stock. I have a lot to learn about diesels and I don't have a local diesel garage to turn to. The dealers won't do any mods.. I'd like to get more towing power out of her but hate to screw up my truck trying to do it.

Looking at the triple column mount.. Are the gauges different sizes or is it the design that makes them look that way. What are they from top down? The top gauge looks like it would be in your face while driving? Does it take a lot of getting use to?

Thanks again for the help..

No. The gauges are all the same size. I just held the camera up close instead of zooming in. They aren't in your way at all. I am only 5'8" but I also don't sit close to the steering wheel. I am about one and a half to two feet away from it. The top one is pyro, middle is boost, and trans. temp. is on bottom but you can put them in any order you want. I remember on my 69 El Camino I had my gauges mounted at the bottom of my dash. But it is really nice when you are towing up a 6% grade with lots of turns to be able to just glance left and see what is going on gauge wise. Maybe I'm just getting old. Just spend some time looking around the forums and Kennedy Diesel and Heath diesel I have bought stuff from. I got my exhaust from Warpspeed Performance, was happy with it. There is also SS Diesel.