Strange transmission behavior

Messages
6
Location
Oregon
Hi all, I realize this may not be the most appropriate place for this question, but the people over at the Buick Forums weren't very helpful. We have been having some intermittent transmission issues over the last year in our 2006 Buick Rendezvous 3.6L AWD with a 4T65e with just over 120,000 miles. First it was a P0741 and no lockup very intermittently on the freeway. The first time was coming down from Portland to Eugene on I-5 in about 60 degree weather, and the other time was in Nevada in 95 to 100 degree weather. These are the only times I have noticed it, it may have happened other times as well. Each time I pull over and scan it with an Innova 3040 and get a P0741 pending DTC. Later this summer I replaced the radiator and put some Valvoline MaxLife ATF and Lucas TransFix in it, and it has not returned since. I am not sure if it is related to running a little cooler or the different fluid. The fluid that was in it before only had about 18,000 miles. It did not smell burnt or have any abnormal coloration. The other issue that has been more noticeable recently is a soft and slow 1-2 and 2-3 shift once the vehicle reaches operating temperature, usually after cruising on the highway for a little while or after driving around town. It also usually has a soft TCC lockup after it has been driven for a little while when getting on the highway. I installed a TransGo shift kit (just the accumulator springs in the pan, not the side parts) and did a fluid and filter change and it did not help very much. If anything, the shift kit made the 1-2 and 2-3 shifts a little softer. The shifts are crisp and smooth at cold temperatures. Any help is greatly appreciated!
 
Messages
1,509
Location
gulf coast FL.U.S.
Computer controlled trans in Buicks and most other Gm lines are programmed soft for an unnoticeable shifts .The pcm /trans need reprogramming to work with a shift kit,line pressures,valve body mods ..there's a lot to it.It all works together as a tightly controlled sequence. The 'puter is trying to soften the very shifts you're trying to firm up ,i believe. Also the TCC has a variable lock-up (based on conditions), or lack thereof.
 
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