2004 4l80e hot trans on hills

It sounds to me like the torque converter is UNLOCKED. You may have to be in--tow haul, locked in 3rd, and be above 40 mph to keep it locked.
My Cherokee is that way. It will lock only above 40 mph in 3rd and in 2nd if you rev it that high. Speed related.

Get a new cooler or quit worrying. I just cover mine with my hat when it reaches 225.

Dannyabear1 wrote:
I would never flush a transmission, that washes all of the junk to places it wouldn't be otherwise, probably blocking most of the cooler; just drain and refill,change filter, a couple of times if need be..

Exactly my thoughts. I can't count the tranny problem threads that start off with " flush", most of em 48RE related with a tuner :W
Drop pan, change filter, adjust bans if needed and drop PM rate 10K miles.
But since it just started up I'd also look at what ATF they used. Trannies are picky that way.

On my previous 02 6.0 4l80e, thenTC began to slip and would not lock up in 3rd. My tranny during this was running hotter then normal and had been for some time. I had it looked at and discovered that during a few years, gm installed some defective TCs which would crack and lose fluid. Sure enough when mine was pulled that was the case. So while it was already out I had the whole tranny rebuilt with a shift kit for around 1700.00. Afterwards even with the stock cooler, it never ran hot, and I never saw it go above 205 even pulling heavy. This was my experience, otherwise the 4l80e is really stout. In fact when we checked the forward clutches, they were barely burnt/worn. But I knew the TC was shot so it was just a few more bucks for a compete rebuild. Anyway good luck on your search. Mine had about 160k when I had issues. Only have a trusted shop look at the tranny and show u the issues if any.

I am with MitchF150 on this...

MitchF150 wrote:
My guess is that it might be in 3rd gear and you may even have the gear shift set to "3", but the TC is running 'unlocked' to be able to hold your speed??

PAThwacker, what RPM's are you running when the tranny heats up?

Yep, trans cooler. Flush it independently or replace it is where I would start

tekman, not sure what the power steering pump has to do with trans temp, there is no collant circulating in the PS pump.

I thought it was just me? :h

tekman, not sure what the power steering pump has to do with trans temp, there is no coolant circulating in the PS pump.

PA, normal temps should be 150, 175 when towing and 190-200 on a steep hill with the trailer. What I would suggest is having the cooler lines disconnected from the trans and power flushed separately to remove any debris.

Not sure about the 6.0 but on my 8.1 there are two coolers in series. the trans fluid goes from the 4L80E into the right side of the radiator, then from there into the aux cooler as pictured above, then back to the transmission. The radiator helps bring the trans fluid up to temp in winter since the coolant is hotter than the trans fluid and helps to warm it. The aux cooler on the front then helps to moderate temps.

I'm curious, are you using Dex III or Dex VI? Dex VI wasn't introduced until 2006 but is now the recommended fluid for GM transmissions that previously called for Dex III. Dex VI is full synthetic and runs a bit cooler than Dex III.

my 2008 5.3 v8 screams up the same roadway. i knew i was cooking the trans when towing the pup.

it sucks when you need a diesel tow vehicle for closest 5 miles to your house!