Question after 48re rebuild

If you did a shift kit remove the check ball for better cooling flow.

The trans cooler will not drain with just the lines off, you will have a quart or so of stuff in there and any accumulated junk. The cooler itself is hard to flush due to the thermostat in it. You almost have to take it out to flush correctly.

Failure to replace or clean it will void oyur warranty at a lot of places becasue it can hold a lot of garbage.

The lines to the front cooler and the heat exchnager are easy, just flush the normal way to clean them out. You have to take the line apart where the check ball is to do it and that leaves the cooler and the short chunk with the check ball that is hard to flush.

There is a thermostat in the cooler that close and bypasses fluid when it is less 140 degrees. Your flush will be less and it will just clean out the the bypass tube, not the main body of the cooler. You have to back flush to clean out the main body and that goe sintot he check ball line and the check ball stops the flushing so you need to remove that line also. All the lines are pointed into the engine bay so it makes it tough to get any type of flushing done on it. Most places just replace it because it is cheaper than the labor to do it correctly.