4t65 weak grip in 4th/tcc

[rick444]

Used uplander 3.5 holds good in other gears.
I pulled pan and is really clean at 120k. Very little deposit. Put new oil/filter on.
I suppose this means things arent too bad. No friction material mud or shavings.
I can live with it but should i drive in 3rd gear and accept the gas mileage loss?
Is there anything that will give 4th a better grip, like a brand of fluid that grips better.
I do not want to take it apart, since it functions so well up to 4th. 4th locks and unlocks like every 5 seconds.
I do not see any codes, but I do not have an advanced readout to study trans as of yet.
I might buy one though because this is interesting. It seems both tcc and 4th clutch slip.
I need to instrument it somehow. Tach alone is not enough.
Any ideas?

[rick444]

Well, whatdayaknow, I waited a month and it seems that the Lucas fix softtened the 4th clutch piston seals enough to stop the shift cycling between overdrive.
My fluid is half dextron 3 and dextron6. Heh, Lucas told me on a call that I should not add their snake oil to dextron 6. Maybe it is compatable with my half and half mix fluid of 3 and 6. Things are looking up at 123000 miles. Works now like new.