New Truck & Trailer 1st tow....????

[zogg]

We finally got to do our fisrt camp session over this weekend. Went 250 miles and all went well, but I do have a couple of questions.

Our travel trailer weights 7300 pounds dry, so I estimate it was about 8200 pounds. The truck is an HD 2500 GMC 6.0L gas with 6 speed tranny and 3.73 gears.

Overall it towed fine, but this is my first GM truck and just making sure it is ok. I towed in Tow/Haul mode the whole time. Left it in Drive. Drove about 60-65 mph on both 2 lane and 4 lane roads. The roads were pretty flat with some small hills, but nothing big.

Once rolling, the truck would run in 5th gear at 2200 rpms, and stay there until it came to a hill. Then it shifted to 4th at 3,000 rpm to pull the hill and shifted back to 5th once we leveled out again. It worked exactly the same whether the cruise control was set or not. As we came to some rolling hills, it continually up shifted and down shifted.

Does this seem normal to anyone towing a similar unit? Seemd like a lot of shifting to me, and running at 3,000+ rpms was a little uncomfortable at first. The truck has 48,000 miles on it, so I did change the fluid prior to the trip.

Second question....when we bought the trailer and brought it home (40 miles), it seemed to porpoise quit a bit. I bought a set of Airlift airbags. I ran them to the campground at 30 psi, and the truck seemed to bounce. I lowered the bags to 20 psi on the trip home and it did porpoise again, but not as bad as without the bags.

Should I try 40 psi on the next trip? I am not sure how to set these up, as it is the first time I have used them.

Thanks in advance for any help and/or advice....Dave

[mcsurveyor]

Engine and transmission behavior sounds normal. You probably won't see 6th gear much. With a 4.10 rear you'd hold it more. The porpoising could be worn shocks, WD bars set up wrong. You might as well try running higher psi in the airbags, though that will probably take tension off the WD bars.

[APT]

Screw the air bags. Replace the crappy OEM shocks. That is the job, to dampen the springs. Air bags like springs just reduce the amount of travel for the same amount of weight/force.

My 6.0L/6-spd tows the same way. Except I use Tow/Haul mode and M5 to lock out 6th gear. It will shift into 6th gear over 60mph, but cannot hold it. 3000rpm is fine, so is 5500rpm. The engine's peak torque is over 4000rom and really wakes up over 3000rpm. Let it spin.

[pitch]

I'm thinking that 5&6 are both overdrive gears and tow/haul maybe locking out 6?

[JustLabs]

I find it hard to believe that on a 2500HD you need air bags with a trailer that size and a W/D hitch.

It seems really odd that you'd need anywhere close to 30-40 psi in the bags.

I'd guess that you need to fine tune the W/D.

[fla-gypsy]

You shouldn't need airbags on that set up. You need to get your WD hitch adjusted properly to eliminate the porpoising. I am confused by your statement that the truck never makes it to 6th gear. You said it was either 5th or 4th. That does not sound normal to me.

[zogg]

goducks10 wrote:
Typical gasser on the shifting. On the porpoising it could be several factors. What's your tongue weight? Maybe get the TT weighed and see where you are with weights exactly. You may have the TT loaded with too much in the rear and not have enough tongue weight. Are you WD bars strong enough? You need to get the TT weighed to find out if your WD bars are strong enough. Airbags won't help with the porpoising. And last are you getting enough tension on the bars?

I changed the transmission fluid with synthetic Kendall dexron vi, the oil with Kendall gt1 full synthetic 5w30, and the engine and tranny filter. I do plan to change the gear oil next week....

[goducks10]

goducks10 wrote:
Typical gasser on the shifting. On the porpoising it could be several factors. What's your tongue weight? Maybe get the TT weighed and see where you are with weights exactly. You may have the TT loaded with too much in the rear and not have enough tongue weight. Are your WD bars strong enough? You need to get the TT weighed to find out if your WD bars are strong enough. Airbags won't help with the porpoising. And last are you getting enough tension on the bars?

[goducks10]

Typical gasser on the shifting. On the porpoising it could be several factors. What's your tongue weight? Maybe get the TT weighed and see where you are with weights exactly. You may have the TT loaded with too much in the rear and not have enough tongue weight. Are you WD bars strong enough? You need to get the TT weighed to find out if your WD bars are strong enough. Airbags won't help with the porpoising. And last are you getting enough tension on the bars?

[Norskeman]

I run the air bags at 45 lbs - but then I have a fifth wheel. Between the air bags and the hitch I think the sag should be out of the back end of the truck.

You may need new shocks too - I have a 2011 3500HD SRW and I changed the shocks at 22,000 miles - made an improvement in the towing. I put on a set of Bilstein front and rear. Good price at http://www.kennedydiesel.com

When you said you changed the fluids - engine, tranny and rear end?

Tranny - I use TranSynd - synthetic tranny fluid.
Front and rear diff - I use Mobil 1 75X90 synthetic (fluid should be changed after the first 600 miles of towing)

[rhagfo]

Does the trailer have shocks?? Shocks on the trailer will smoth out the bounce.

[kw_00]

Dont let the RPM scare you, its working near its rated TQ RPM around 4K. With the 6 speed your sure to have a great truck, compared to my older 4speed. Enjoy the ride.

[Dadoffourgirls]

The truck is behaving as expected. On rolling hills, you would need to drive with foot and not cruise if you were willing to lose speed going up.

As for the porpoise effect, what hitch and what bars do you have?

On my 32BHDS, the dealer installed the 800 - 1200 bars for my hitch, but when I changed to 1000 - 1400 bars the porpoising was reduced significantly.

[jbardram]

Congrats on the new trailer!

The shifting and rpms sound normal to me. Sometimes in hillier terrain ill lock ours out of 5th and 6th to avoid some of the unnecessary upshifting.

The porpoise effect doesn't sound normal. I don't think you should need airbags with that trailer. Is you WD hitch setup correctly?