Oobray

Well, hooked up my camper for the first time. I have an 02 Yukon XL with 8.1 and 3:73's. Camper weighs about 6,300 lbs. After about 50 miles of not being able to maintain 70mph I manually put it in 3rd and cruised between 2,600 - 3,000 RPM and it pulled pretty well. What was weird its that at 70mph with the pedal fully depressed and the vehicle losing speed it would not shift out of OD. It appears my "sweet spot" for towing power was around 2,700 RPM. Is it safe to tow here? I'm not sure if the TC was locking or not, but trams temp stayed right around 200deg so I guess it wasnt really slipping much. Is this normal for towing with the 8.1 and 4L80E? I'm wondering if I need to drop the money and re-gear to 4:10 or 4:56. I don't do much hwy travel in this truck unless I'm pulling the camper.

DEWFPO

It'll run that rpm all day long without problem. My '05 pickup with 4.10's runs 2500-2600 rpm at 75 mph.

DEWFPO

Oobray

So it's normal to have to tow 7k in 3rd at this RPM? I just filled up and did the math I got 5.5 mpg!!!!

Whipped383

7k should tow with ease but not with your gears. And 5.5 mpg? I get at least 6 with almost double the weight and climbing alot of steep grades, I live in the rocky mountains

Vindii

It not normal for it not to down shift when it needs to. You should not have to leave the shifter in 3rd gear. I've tow'ed a 10K enclosed car trailer a few times and it stays in OD until it needs to shift out.

Did you have tow haul on?

Somethings up with it not letting it downs shift by its self.

Doc_speeder

iTrader: (1)

Any codes or CEL? Just comparing to my 6.0 4L80E combo, but it sounds like you're way down on power/torque and something's up with your trans. You should be able to maintain 70 mph in OD with a trailer that light unless you're in the hills.

Oobray

I don't have a code reader but it's not showing any CEL or anything. I just made a 600 mi trip without the trailer and got almost 13mpg. I did realize that my speedo is off cause I have 265 tires instead of the 245. But only by a few mph. But I guess that can make a whole tanks worth of mpg calculations off cause I'm going further than I think. I've got it scheduled for a complete tranny rebuild this week and I'll get a black ear tune after that. Hopefully that will help out.

Doc_speeder

iTrader: (1)

Why scheduled for a rebuild? If it's sensor/ECU/tune problem, the rebuild will only be an expensive stab in the dark, and the problem may still very well be there after the big bill is paid. Why do you think it needs a rebuild?

If It's not slipping or running too hot, I would definitely pursue some other diagnostics first. It should definitely be willing to downshift if you put your foot to the rug. Something's up for sure.

Same goes for the Black Bear tune. I've towed with an 8.1 a couple times. You sound like you're down on power compared to just a good running stock big block. If you get a tune and don't fix the problem first, you're just asking for disappointment.

Oobray

I scheduled the rebuild because it's slips going from 3 to 4 when accelerating hard and the fluid is really, really dark. It's got 200k on it. I'm also wanting to be preventative because I only drive this thing when on road trips and pulling the trailer. So it going tout would be really in opportune. This most recent trip I was pulling a 15' Uhaul with some furniture and it downshifted fine. I think a lot of the problem with my travel trailer is LEO that it's 14' tall and almost flat in front. That's a lot of wind resistance at 75mph. Because I just realized my speedo is off I was pulling at 75-80 when I thought it was 65-70.

Vindii

I agree with above. These trans seem to hold up pretty well. I haven't heard of anyone having one fail yet.

The height of the trailer wont make it not shift. It will just want to shift more due to more drag.

Did the trans shop do an inspection? Did you tell them what its doing? Or just ask them to drop in a new one?