I suspect there is a sticking valve in the valve body.

These are aluminum bodies and the valves can get a rough spot in the valve bore due to debris circulating in the oil.

The only real fix is going to be to remove the valve body, totally disassemble it and locate the offending valve/bore

First I would drop the pan carefully and see whats in the bottom.

If you find a serious amount of metal crud, then herein lies the issue.

The 700R is picky about having clean oil.

Older boxes like the 400 are more forgiving of dirty oil than the 700R

Hope this helps

Missy