You could try upgrading to Radio Stack 4.21 to see if it helps. Some signal strength issues were resolved from 4.16 to 4.21, I think.
Also: if you're using a 4.x (WM2003) ROM, signal strength went down when you switched. This is just a change in how signal strength is displayed, and does not reflect a change in the level of signal received.
(Please be aware upgrading your Radio Stack comes with certain dangers, and that the procedure to do so is not well-understood, and that we, or anyone else, can't help you in the event something goes wrong...)