I was just reading through my 2007 Ford E-series service manual. I noted the following service intervals for our TorqShift transmission with OEM external bypass filter, a bell jar design.
Under normal operation.....
At 30,000 miles, drain the oil using the drain plug and replace the external bypass filter. Leave the inside filter alone, no need to replace it yet. You will need 9 quarts of Mercon-SP transmission oil.
At 60,000 miles, replace both the external and internal filters.
At 90,000 miles, replace only the external filter.
At 120,000 miles, replace both filters
....and so on....
Under extreme operation, everything changes to 15,000 mile intervals. The choice is yours if you want to consider your PC operated in "extreme" conditions. It just might be.
Here is the bypass filter. The last year Ford used it was 2007.
The filter inside looks like a roll of toilet paper. The filters are available at most auto parts stores, though you might have to order it at some places. I bought my replacement from Autozone, the Duralast brand.
The instructions say to NEVER drive the vehicle without the bypass filter. Being a bypass filter, it is safe to operate the vehicle with an extremely dirty plugged-up filter, but driving without the filter, the transmission will get damaged because most of the oil will pass through the bell jar instead of through the transmission oil cooling system.
This bypass filter when new allows 10% of the transmission oil through it by design. As it gets dirty and slowly clogs, less and less oil gets filtered through it.
Unlike the primary internal filter, the bypass filter captures extremely small impurities, so it's really nice to have. It makes sense to replace this filter every 15,000 miles, per the "extreme operation" service interval.