The dishing problem can be caused by a different speed in the heat exchange of the upper and lower mould and/or by the combination between the mould profile and the integrity of the plates of the press you are using. Wrong settings in the I/O hoses for steam and water will result most likely on warped records, not dished records.
1. Have you checked the hardness of the water you are using to cool down the record? Dished records are the very first clue of a bad heat exchange caused by the hardness of the water.
2. Cut a record with scissors and measure its thickness in the center and in the edges, using a Vernier gauge. Not in the grooveguard area of course, but just in the center and in the outer edge. If the difference between the edge and the center is .02 mm or more, then there is a problem you have to correct. This test is normally done to check why records tend to warp, a different problem than yours, but it might be very telling for your issue too.
If your record is dished, and you hit it with your finger in the center just like you want to "correct it" to bring it to the proper shape, and you see that it gets flexed, but at the same time it makes a sort of "click" and goes back to its original shape, then it means that it is too weak in the center. Most likely, you will find out a remarkable difference between the thickness of the center and the edges.
If your moulds are new, I suggest you to check the plates below the moulds. And the heat exchange.
Assuming that the heat exchange is OK, if you want to try an immediate solution, just to test: take two nickel mothers, cut out their center, keep just their outside diameter (let's say a 13" wide outside circle and a 10" inner circle) and place them below the moulds. If the records come out flat, than it means that you have to rectify your press plates, to make them perfectly flat. It's a 500$ job here, maybe you can find there a cheaper solution.