It sounds like you guys are saying that if one adds perforated tile to the lowlands, that will allow more water to drain out of the lowlands.............and...........since the tile from the uplands is hooked into the lowlands drainage, the uplands water cannot escape due to meeting up with increased lowlands water......and thereby forcing the water from the uplands back towards the uplands...............right??

So.........even though it would most likely be expensive........(but maybe if drainage is achieved, the tile cost would effectively be nominal)..........................the fix is to use, effectively, two systems....................one a non-perf pipe thru the lowlands, used exclusively to hook to and drain the uplands...................and the other a perf system to drain only the lowlands.

It's an escape problem..............up-pipe water cannot escape if more water is added to the down-pipes.

??