GMC surging while pulling trailer upgrades

Rex Marble · July 18, 2024

First time pulling a trailer with 1/2 ton GMC suv. When starting to climb rolling hills the GMC starting surging. The surges were quit noticeable and concerned that the truck to stop but it continued to run while surging and speed reduced. Once on the top of the grade the surging stopped but engine didn't seem to have the normal power. The tach did not vary during the surging. Does the issue sound to be more engine or transmission issues?

CamGTP · July 18, 2024

How heavy was the trailer? DId you check on the dash to see your transmission temps at all?

Usually the tach would move some if it was surging, because either the engine is being lugged down or the transmission is slipping/torque converter issues.

You could also have a trailer brake be an issue as well. The brake could be dragging and releasing on an incline and that is what you are feeling. Hard to say at this point without driving your truck and see it happen in person.

Rex Marble · July 19, 2024

The trailer is 4800 lbs. The transmission temps topped out at 248 degrees. I have been told after getting home that the transmission temperature should not have been over 224 degrees.

I thought that the tach should move some also when surging.

The brakes could possibly be an issue, because the sensation was similar to what I think the fill would be hitting the hand brake while in motion. After purchase and before getting on the road we did check the hand brakes to be sure that they were working, and they were. Is there something on trailer brakes that is activated when not on level roads? I did read on a post where someone disconnected the cable to the trailer to test the possible brake activation; their results were negative but something I should check.

I will check the brakes and see what the results might be. Thank you for your response and suggestions.

My son is out of town for about two weeks. I will post the results of the after the test.

mikeyk101 · July 19, 2024

I only saw that kind of trans fluid temperature and higher while climbing 7-8% grades in Bighorn Mtns in WY. Partially my own fault but that's another story. My 16 Silverado was pulling my loaded toy hauler that weighed somewhere around 6200lbs. Regular rolling hills have never gotten that high.

What kind of controller are you using for the trailer brakes? Is it an OEM built in or an aftermarket? Could be a problem with the controller?

I would say though,that if it was the trailer brakes dragging or locked up, you should at least be able to smell it or see some smoke coming out from behind the wheel(s).

Edited July 19, 2024 by mikeyk101

CamGTP · July 19, 2024

Yeah, those transmission temps are way too high. You need to install the lower temp transmission thermostat from GM or do the thermostat mod to stop it from working and have it flow fluid all the time. The thermostat mod will reduce transmission temps under normal driving condition by at least 30-40 degrees.

It can be 80 degrees outside and I'm cruising down the highway with temps in the 140's.