i'm in the process of installing the sonnex tricumulator valve, extra trans cooler and external trans filter. should i install the new cooler with the stock cooler or remove the stock cooler and just install the new one? does it matter what trans cooler line i install the external filter on?

 

I replaced the stock cooler with a new Tru-Cool, because the Tru-Cool is all you need, and the stock cooler would merely be another source of restriction for the pump to overcome. Besides, the stock cooler makes a great PS cooler. I installed a new Magnefine filter in the line leading to the intake of the cooler, so I can keep the crud out of the cooler.
If the cooler you have is a Tru-Cool, you'd definitely want the intake line coming in the top of the unit. It's got an internal bypass system in it that will allow the tranny fluid to pass through the cooler without going through the main body of the unit, so the fluid can get up to operating temperature.

 

DITTO Quadzilla!