Reverse gear gearing is almost the same ratio as 2nd gear. 5 percent isn't much but when you add that load it is.

Some people walk like an Egyptian. I walk like the pope with a cane.

 

Is that the dry weight of the trailer? You may be pretty heavy with gear loaded in it.

Have you changed the tranny fluid recently?

It makes sense it will hear up more while backing since when driving on the highway you have airflow across the radiator, but won't have this when backing.

It is odd that it heats up that quickly though.

 

If I'm in an area with a dirt or gravel surface (not pavement), I put the truck in 4-wheel drive, low range before backing with the trailer. This takes some stress off the transmission, and it seems to make it easier to aim the trailer.

 

This is what I do also. On a 4x2 I don't know how to work around the problem.

 

Besides that trailer is most likely over the max weight compacity for a 1/2 ton ( just length alone you are a brave person).
Backing up with no airflow and a heavy load is a recipe for transmission overheating regardless of the size of the tow vehicle. You can try to use 4wd and be quicker or get a cooler that has its own fan might help.

 

no 4 wheel drive. There is 43K miles on the truck. Been tossing around the idea of a fluid change and upgrading the inter cooler. Sucks that Nissan didn't put a fan on it. Also that its on the small side.

 

I have had this happen several times with about the same grade. My trailer is only 26' and weighs 6200lbs loaded. These are also short back ups. I'm afraid to take the trailer hunting as I will either have to back in or back out about 35yards. Dang Nissan.

 

It's not just a Nissan problem, I had a 1ton Dodge that did the same thing. Reverse gears are high and add the lack of airflow means a hot transmission.

 

Something isn't right. Sounds like you were running hot prior to backing it up. 90ft is not really that far for the temp to jump like that. Maybe the gauge is off? If it doesn't shut down or redline just back the sucker up and if you want, let it idle and cool while you unhook.

The only time I had an issue with tranny temp backing up was after a ton of towing real steep hills on approach and inside a campground at low speeds. I was pretty hot per the gauge before I even started to back it in. Even then it didn't overheat, but was def pushing it.