Did you try the great 727 modifications from the forum guys around concerning the actual performance of the 727?
I must say that I was sceptical first but now I'm a big fan of them and drive my 727-100 and -200 with those fixes.
The thinking behind those fixes is to make the plane behave just like mentioned in the performance charts and, aside from Lou's great tips, those are a real help then.

As both things are freely available, they are more than a tip.  :)

Below a certain speed you will enter the vicious circle of high drag leading to even higher drag, I think.
Since you are writing about some high throttle setting, you might pitch up when you see that you are descending to fast. This pitch will (first) lower the descend rate but then will significantly raise the drag value because of the now higher angle of the nose, so you are slowing down some more, leading to a higher descend rate which you then counteract by pitching even more up, and so on. Thrust is limited, drag can raise to enormous values though.
Especially with those mentioned free modifications of the 727 performance, you will find yourself being able to hold a steady pitch for "flying on the runway" and also getting the control over the descend rate by just the throttle setting, leading to a nice and "clear" descend.