06 Chev Express 6.6 tranny #5 Help!

[likearok]

We are baffeled! Have had tranny problems since 40,000kms, when they rebuilt it first. Then @ 140,000 kms the rest came and smoked them all. Basically Since 40k ONLY when outside temperature was above 90 f tranny would slip and this problem is still occurring. 3rd gear has gotten welded from the heat twice and in 3 days. Yes 3 rebuilt trannys in one week and currently we beefed up this 4L80E with a competion racing kit, tweeked the hydraulics to bring up pressure between shifts. put a high flow external cooler and temp is down. Yes this is a bandaid but until we figure it out ??? Next step is electrical and we ran scans and guages while driving and typical stock readings and no codes no glitches. Looking for some input 4 experts are baffled as well. Look forward to some remmedies.

[87max]

I would put in a tranny gauge so you can have a constant monitor on the temp & that will help you diagnose as to when heat is building. New converter? If it's shot that will wreek havok.

[More Power]

Is the engine running with stock power? The 4L80-E's input torque limit is nearly maxed with the stock Van Duramax.

Jim

[likearok]

Well I am aware that the TCM is limited to it's output ( especially pressure output ). Yes GM wants to hold the horses to save the tranny. Thats one reason I did not chip the truck. if Allison was available or could convert I would. TC was changed twice. Outside of spending a fortune on a racing tranny I am still looking for a real fix. Yes I have ordered a temp gauge and a tranny pressure gauge $200.00 wasted but necessary in this case. Thanks for your replies & keep them coming.

[twaddle]

This is a longshot but were the transmission cooler hoses changed at the same time any of the work was done on the tranny?
I'm wondering if the inner wall of a hose is collapsed in restricting oil flow to or from the cooler causing overheating on hot days due to reduced oil flow at the cooler. The higher temperatures would lower the viscosity of the oil dropping the pressures. I would recommend using a synthetic transmission oil as this would be more stable at higher temperatures than the standard oil.

If three different trannies failed so quickly and no parts were reused from the old units then it has to be a non internal fault. Was the torque convertor changed each time?
Is the tranny changing through the gears at the same engine revs and is the engine revs he same at certain road speeds as it did before 40,000kms or have you noticed any difference.
Any fault codes showing from the transmission ECU?

Good luck

Jim

[likearok]

Unfortunately there has been no codes since the original at 40k. We have bypassed the original cooler and put a larger high flow in and is currently functioning but I feel some harsh shifts rarely and its hard to monitor right now with a racing kit as it performs completely differnt from stock. I would like to chip the truck but really should find the problem first.