I have a problem with the A518 automatic. For a year I’m driving with the A518 od/lu trans behind a 408 stroked engine. It works fine but after 1500 mile the trans start making problems. when the engine/trans is at operating temperature it just shifting up late and downshifts early when I'm letting off. When I’m driving at a constant speed it will downshift from 3rd to 2nd gear. When I turn the gas it shifts back to the 3rd gear. This happened at speeds between 2000-3500 RPM, even if the automatic is in overdrive. Oil is ok, kickdown adjustment is ok. Oil pressure is 80 psi, there is no change in pressure when the problem occurs (unasked downshift 3-2)

Its a A518 od/lu with A618 internals and a SF TFOD-jr shiftkit.

Any help is welcome, thanks.

Patrick