2002 siverado transmission failure #3 (21k m.)

Transmission is starting to fail again for the 3rd time. Previous history of this tranny at following link. www.talkabouttrucks.com/group/ alt.trucks.chevy/messages/68716.html
Truck has 34k km. (21k miles) on it now.
Took it to another dealership under warranty. They took it out for a test drive and found no problems, also no message codes came up.
These are the present observations.
On occasion after coming to a stop and then proceeding again, tranny will slam hard into gear at start and then operate normally in 1st and 2nd gear.
Most of the time when tranny is shifting between 2nd and 3rd there is a slight rev-up of engine for a second and then it will engage properly in 3rd. ( tach shows a slight rev. increase )
All the time when starting out on the highway, tranny will stay in 3rd gear for approx 20 min. and then sometimes shift into overdrive. Tach will read 3400 rpm speed 110km/hr. When it was operating normally? it used to shift into overdrive at 70km/hr. and up under normal accelleration.
Last dealership when they took it out for a test drive never took it above 70km/hr. This is after I told them about the above problems.
I'm taking the truck back again next week and would appreciate any info. that anybody can give me that I can forward to the service manager as to how to fix this tranny once and for all. These people need all the help they can get.
Talked to a couple of tranny shops in Edmonton but there is nothing they can do while the truck is under warranty.
The most weight this truck has ever hauled is a 1200 lb. boat.
silverado cew cab LT 1500HD 6.0L engine 4L80e tranny
If it wasn' for all the tranny problems I'm having, this would be a great truck. I also realise that the tranny is one of the better ones to have since it is the one that was the most reliable in the service trucks that are used in the oil patch.
thanks in advance
frustrated in Edmonton. Alberta . Canada
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Try using a vidio camera. I did this with my POS DODGE DAKOTA (Worst vechicle I ever owned) I had a beautyfull clear malfuntion on camera and they still said piss off. So much for warrenty It means nothing if they wont

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