My 08' w/3.5L sedan has the 4L45E and it seems to lock up soon but the car is light and the engine has good torque for the weight it's pulling around. I've found it to be near perfect (for a GM) as is. Are you sure you have the 4L65E and not the 4L45E? I had the 4L65E behind a 3.4L in my 00' Venture and it was starting to have line pressure problems at 140K miles shortly before I sold it. The problem was apparently common and required replacing at least one solenoid and likely wiring that had been cooked for years in the side case.
unlikely youre still around but im curious about these parts and what happened with you, similar thing here 09 3.5l 4t45e having problems with lockup trying to increase speed slowly the car will shudder and in reverse sitting still it does the same shudder randomly. only at 58k milesYes my bad it's a 4t45e transmission. I've been looking at New solenoids and sonnax parts.
It seems like a pressure issue from what I gather. Sonnax builds a drop in part to fix the worn bore inside the valve manifold. This makes sense because if "I put my foot in it" the tcc responds corectly. Is there anyone who has experienced the same symptoms, who would like to share how they fixed the problem.