is HP tuners right for me? minor trans issue at idle

The vehicle is a 2007 Buick Rendezvous with 3.5L and 4T65E. (Is it supported? I see the 3.6 and 3.4 listed for Rendezvous, was 3.5 overlooked, or not supported?)

The crossover has never trailered and generally been driven in an average manner (Ohio temps, no hard acceleration, mix of city/highway miles, etc).

I did the first transmission pan drop and filter change at 50,000 miles. I used a real ACDelco filter and Dexron VI as called for.

With a pan drop, I am swapping 8 quarts at a time, from a total of 12 in the system.

There was a light amount of fine paste in the pan and on the magnet.

Around 65,000 miles, I first detected a slip. It happens when you pull away from a red light or stop sign. It is like you are in neutral, no movement at all. It lasts only a split second and then there is a bang and it catches and goes. The weird thing is, there is no rhyme or reason to when it would slip. It does seem more likely to happen when hot, but has done it cold. It could slip 5 times in one day, and then not slip once for months.

At 75k I did the second pan drop and filter replacement. Pan and filter (I cut it up) and magnet all very clean. Fluid had no burnt smell or appearance.

I'm at 93,000 miles now. So it's been doing this for about 30,000 miles now.

A couple months ago I took it to a local independent trans shop that has a good reputation with car guys I know. He connected a scan tool (sorry, not sure which one) and we went for a test drive. It wouldn't slip for him, of course. Subjectively he felt the trans was operating great and the scan tool didn't reveal anything. He looked at the fluid and that seemed good to him as well.

I do want to keep this vehicle for the long haul. Other than this problem, it's probably been my most dependable car purchase ever.

One theory I've been given, is that at idle, the line pressure is very low, and there is a seal somewhere that is slightly leaking fluid past it. Until I step on the gas and pressure builds, car doesn't move.

So I was considering a very slight increase in pressure. Preferably only at idle -- if that can be done by HP Tuners? I would try adding say 5%, test a few weeks, then add more if still needed. From what I have read there is a huge disparity in pressure at idle when in "D" versus "1". So I would not think I'd be doing any damage by increasing it slightly.

Thoughts?

Thank you!
Brian

Brian, I would go the easy route in your case and for now - keep doing what you're already sure you should be doing. Getting a second opinion! It should cost next to nothing and be little trouble in the long run to have one more shop take a look, just my opinion. Not trying to dis your shops skills, more like playing it safe for now. I would see if any city around you use Impalas (4T65E based) for their police fleet, find out where ALL of them are CONSTANTLY getting their transmissions fixed - then bring your Rendezvous there for your second opinion as they should be virtual experts on 4T65E's by now. Also not trying to turn you off to tuning, just from tuning something without it running like it used to before the tuning process even begins. If all else fails and it's driving you absolutely crazy then sure by all means explore some more alternative aftermarket methods of approach. But It sounds like this is a softly driven daily driver. So I wouldn't go throwing too much money down that path just in case something actually is wrong with your transmission that you can detect, being the primary driver of the car for some time now. I could sit here and recommend all sorts of cool stuff to hook up that transmission, ( ZZP shift kits, 5.3 V8 Impala final drives & shafts, HP Tuners, ect...) but face it that stuff adds up. On the other hand, if this is a solid, clean, rust free vehicle you love and want to keep for quite a while longer - strongly consider going for a full transmission rebuild first. You've gotten enough miles out of her already so it's not like its a waste, and it's not like you haven't tried a pan drop yet. Plus everything would get opened up for a detailed visual inspection. And if you saved up enough extra money, that would be the optimum time to install aftermarket parts for future "insurance", as well as added toughness.

Dr. Nopps-

Just FYI - I've owned this vehicle since new. Thanks.

I would buy a bottle of "Lucas transmission fix" and give it a try... it would help seal any internal gaskets. if your fluid level is half way up the xxx's on the dipstick (while car is running in park and trans fluid is warm), you should be able to fit 1/2 bottle of the Lucas trans fix... instead of dropping the pan I use a clear hose tube attached to a transfer pump driven by a cordless (or corded) drill and I'm able to pump out around 6 quarts through the dipstick, so you can do the same to get 1 quart out and replace it with the Lucas Trans Fix.... The Lucas trans fix also helps with slipping and hard shifting.