Trans Problems when Towing

[Aepozzi]

Hello Everyone,

I am new to this site. I just joined today. I have a 2003 GMC 1 ton.

I installed the "Powerup Diesel" 80 hp program about 10 months ago. 2 weeks ago was the first time towing the trailer.

The trailer is a 36' Newmar and weighs 13,200 empty and 17,450 +/- when traveling. We departed CA and drove to Seattle, WA. The trip going up went flawless.

Coming home on Interstate 205 near Portland we were climbing a long grade. I had it tow mode, however, I did not take it out of overdrive. I could tell the truck had a load and was working hard. We hit a little bump and it seemed to drop into 3rd gear. The tach read 2,800 rpms at 50 mph. I pulled off the side of the road and received a msg "Shift Inhibited". I shut the key off and re-started. It seamed to run fine until the next hill which it did it again.

I pulled off and shut the key off, but this time on re-start it didn't clear itself. I shut it off again and waited a while. I restarted and it seemed to be fine.

Went down the road some more, this time when I hit a grade I would press the button to take it out of OD. I went a lon way with no problems.

We pull in to stay the night. I crawled under and checked all the connections. They all seemed to be tight.

Next morn. I took-off down the road, in tow mode, with OD on, and it did it again. I had beed watching the Instant Fuel Eco. It seems when the Instant Fuel Eco drops to 4 mpg the trans acts up, defaulting into 3rd gear.

I tried this 3 times with the same results. I finished the trip home pressing the OD button to off when going up a grade. When the instant MPG got to 6 MPG I pressed the OD button.

I called Powerup diesel and tey did have any answers. They did say to install the 70 hp in-place of the 80 hp program. I have. I have not had the chance to take the trailer out. I will at the end of the month.

I did look at all the problem codes. There were many. I guess over 40. I wrote about 30 of them down. I finally deleted the rest.

Does anyone have any suggestions?

I would appreciate it,

Respectfully Submitted,
Andy

[Kennedy]

I did look at all the problem codes. There were many. I guess over 40. I wrote about 30 of them down. I finally deleted the rest.

Does anyone have any suggestions?

I would appreciate it,

Respectfully Submitted,
Andy

And the codes were? DTC list is critical.

I mean I can state teh obvious and that is your power is likely higher than the trans can handle and/or poorly written. This could well be tuning related, but could also be fluid related. Assuming you have done al of your maintenance are you running any special super duper synthetic fluid?

Simplest test is to run at stock power level and see how it does.

[Aepozzi]

The stock power level ran fine, however, at the stock level it would not pull the trailer, and the fuel eco was down to 9 mpg.

When we first purchased the truck it pulled the trailer good. Going to destination 10.5 mpg, and the home trip was 11.0 mpg. It was like this for3 years in a row. Then the injectors went out and we had them replaced. From that point on the power was down as well as fuel economy.

I think I spoke to you regarding a chip and you only re-configure the ECU. With the new CA smog test I could not take the chance. I know I could purchase another ECU,but that is more than I wanted to do.

I don't race. All I wanted is what I had.

Just prior to taking this trip the batteries went completely dead. Some have said that could be the problem. Could be the problem.

Some of the codes that came up are as follows: 0735, 0843, 484D, 5258, 5E64, 6A70, 767C, 8288, 8E94, 9AA0, A6AC, B2B8, BEC4, CAD0, D6DC, E2E8, EEF4, FA00, 060C, 1218, 1E24, 2A30, 363C, 4248, 4E54, 5A60, 666C, 7278, 7E84, 8A90, 969C, A2A8, AEB4, BAC0, C6CC, D2D8, DEE4.

There were more I just deleted them.

The power level I installed was the 80 hp / aprox 150 ft lbs extra tq. I just reinstalled and put the 70 hp level in.

Thank You,
Andy

[Kennedy]

The code list is kind of suspect. Clear then and see what comes back. P0735 is 5th gear incorrect ratio which means slip.

[Aepozzi]

0735. That makes sense. The truck was pulling hard in OD (5th gear). I think when hitting a hill one should take it out of 5th (OD). For me I am towing quite o lot of weight. OD is just to much.

I installed the 70hp program. I wonder if I should put it back to 80hp?

Did you ever come up with a plug-in reprogramer?

With the CA smog law I would think that would be a must.

Andy

[DmaxMaverick]

Don't worry about CA smog, for now anyway. If it doesn't smoke (no load), all the parts are in place, and the SES isn't on, no worries. The inspections are only "visual", in that, no smoke, no codes, with all the smog parts installed (working or not), is a pass. The computer program doesn't mean anything, as long as the VIN matches. If you want the best of both worlds, get a spare PCM and switch in the OEM for testing. Get one on Ebay for less than $100 and have John stick in his best econ/tow program.

[Kennedy]

0735.
Did you ever come up with a plug-in reprogramer?

With the CA smog law I would think that would be a must.

Andy

With the ECM swap you have the ability to simply swap back the stock ECM into place and do your thing. I have not embraced the hand held stuff. I have it available, BUT the tuning becomes a free for all. I consider my tuning work to be sacred and I won't let it out without control. I could release something less special to run with the competitive offerings, but then my capabilities would undoubtedly be measured by my "B" work.

That said, you may well see a handheld offered for LBZ and LMM Dmax trucks as I can control copyright with those platforms.

[More Power]

Hello Everyone,

I am new to this site. I just joined today. I have a 2003 GMC 1 ton.

I'm curious about the history of this 9 year old truck. Have you owned it since new? How has it been used since new? Does it have a history of performance mods? History of trans replacement? How fast do you tow?

Jim