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