Using Sport for your daily commute on city streets is where it will decrease gas mileage, but once on the highway (where the car can justify needing 5th gear) it's not going to change anything. For example, while I was driving down the road doing 45mph, around 2000rpms, if I bumped it back to Drive, the rpm's went down to around 1600 and if shifted into 5th. At freeway speeds it will always shift into 5th, so Sport mode means nothing then other than when it downshifts for passing.

As for the fluid, the thing about LT71141 is that it's designed to have a longer service life...not "lifetime" persay, but longer than a standard oil at say 30-50k intervals. I've read of other experiences on other boards about people even using good ol Dexron and changing the fluid and filter every 30k, all without any issues. The problem is that most of the people on these forums who are even reading about transmission fluid, types, filters, problems, etc are already into the 100k range. As some have suggested here, it may cause more problems than good SINCE they've already got such high mileage and aren't addressing the problem as preventative maintenance, but more as a bandaid for issues that are starting to happen at the present. I have a machine that holds about 18 quarts of fluid, hooks to the transmission lines at the radiator, using a plunger that pulls out fluid and then replaces it at the same time.

It shudders at the same speed/rpm as before the rebuild? I would imagine it's a clutch pack issue...but I'm by no means a tranny expert, I just read a lot. Heck, it could still be the fluid though as I know people have expressed issues on my motorcycle forums about using car synthetic oil vs motorcycle synthetic oil due to the different wet clutch additives. As long as you're using something that says it's LT71141 compatible, and I'm assuming you have a warranty, then I'd just drive it harder and see if something either breaks, or breaks-in...seriously.

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