Re: 545rfe Problems
This problem just started out of the blue, or was any maintenance done?
Eventhough disconnecting the battery will change something in the memory of the TCM, it will not bring the CVI´s (clutch volume indexes) back to basic settings. This can only be achieved by doing the quick learn method using the DRBIII.
I had a rough 1-2 shift after my transmission rebuild and only after the quick learn the shift was smooth again.
But by doing the quick learn you will bring all CVI´s back to basic settings and could eventually cause rough shifting from other gears, but that should smooth out after some driving. Did you check the CVI´s already? (using DRBIII or equivalent)
When you did the fluid change, you didn´t find any loose part in the pan? There could be a problem of a broken spring of an accumulator piston inside the valve body.
I was just looking in the clutch application chart and when downshifting from 5 to 4, it releases the 2C clutch and applies the 4C. The 2C should be ok, otherwise you would encounter problems in second gear as well, but the 4C is only used in 4th gear and second prime. You normally never downshift when in second prime, so you won't see the problem then.
So probably installing the transgo kit would be a good idea, so that you can confirm that the accumulator springs are ok. You will change most of them anyway with this kit.