Looking for ideas.... 2000 Gmc Sierra 3500 Dually, 2WD, 7.4L, 4.10 gears, 56,000 km pulling a 11,000lb 5th. Truck runs good and pulls trailer fine at highway speeds, engine and tranny temp normal. Whe the truck has to pull a long hill, engine temp remains the same but trans temp goes through the roof (auxillary guage). The truck will pull the hill in second or third gear and the TCC is NOT locked up and I know this is the reason for the heat. (Outside temp on the last day was 12'C).

I need ideas on how to control the heat or ways to allow the TCC to lock up. The auxillary fan is already wired with a manual over ride switch.

My initial thoughts...
180'

sorry....continuation...

180'C T Stat
bigger trans cooler (issues with winter or cold temps???)
deeper sump with cooling fins
ceramic coated headers to help with under hood temps
change 4.10 gears to 4.56 gears

Any thoughts or suggestions would be appreciated. Tranny is on synthetic fluid and the fluid never smells burnt or dark in color.

thanks

I know you want the TCC to lockup but if you do you will spell death to that transmission of yours. The computer is doing its job of protecting it.
The heat is created at the torque converter and cooled at the transmission oil cooler.
I know it smacks against logic. the torque converter should be locked up in order to stay cool. In this case the torque converter needs to exhause the fluid. This is the reason why it is taken out of lockup by the computer.
While in hydraulic mode. Not locked up it creates even more heat.
Retrieve codes to determine why the no lockup. If it is simply a heat issue then there could be several things to consider.
Restriction: Where? Filter Trans oil cooler. Between trans oil cooler and radiator could have debris. Get a radiator comb and straighten the fins.
Check Fluid level of the transmission.
Is the transmission temperature going over 295 degrees. This will kick the transmission into hot mode. Yes the transmission can handle the heat up to that point.
If the transmission's temp is somewhat below 295 degrees and into 270 or so then I think you might have a problem with the transmission fluid temperature sensor. You wil receive a code if you pull codes.
The tripping point for hot mode is around 295.

Thanks for the reply....I should have clairified that the truck was only doing 40 km/h, maybe not enough air movign through the cooler to drop the temp.

No codes and I know it was running hot (air lines running along the frame melted through on that pull)........fluid is new as well as the filter......no restrictions as it was flow tested when the tranny was flushed......fluid is still bright red and smells ok......as soon as I pulled over and let it run the temps started to drop immediately.

Could also be that I am now spoiled with the allsion and the fact that the TCC locks up once in second gears and stays locked up.

Any thoughts on my ideas on how to control the heat???

The transmission can handle the heat up in the very high 200 degree range. Around 290. The limit is around 295. One of the best things about the 4L80-E is the fact it doesn't use bands to shift if you are in drive.
I have personally seen a transmission catch on fire while pulling a boat because the bands within the transmission were not holding. This will not be the case with the 4L80-E.
Air lines are not supposed to melt so I believe you were running on the hot side. If you weren't in OD the transmission was likely in "hot mode" Denying mechanical lockup OD.
I take a fancy to GM's methodology in design but they do have weaknesses. Insulate those air lines or move them away from the transmisison lines.
Get a infrared temp gun to monitor the transmission's temperature. I do it. I don't trust gauges because OEM gauges are not calibrated. Idiot lights are never to be trusted.
Oil is an excellent medium to carry away heat. Oil coolers have a bad habit of being undersized or restricted. If that might be the case then place a low profile DC fan wired with a relay and a thermocoupling. If you don't like the thermocoupling then a toggle switch.
There are cases where these transmissions are handling very heavy loads in terribly hot conditions and handle OK.

thanks for the help

Well I looked at several stock tunes with hp tuners and found that with both 8.1 and 7.4 engines in front of these transmissions. They should stay in lock up down to very low speeds once they reach hot mode! (267 F). The 7.4 shows 2nd gear release normal mode 40 mph and hot mode down to 15 mph before release is commanded at all throttle positions. 3rd gear is 40 normal and 20 hot, and 4th gear release 40 normal and 30 once in hot mode. My 8.1 has different speeds for both modes but same idea. It looks to me like the factory wants to keep the convertor locked even more as the temps increase! Hope this helps.