Maybe I'm missing something obvious, but I think the 436 & 536 just scan slower. It seems like the 436 is eventually getting around to what the Whistler picks up first. Do you have the same towers programmed into both scanners? I don't have a Whistler (but I do have GRE and RS scanners), but it seems the Uniden's scan speed is slower. I wish this would be addressed in a firmware update.
As for Virginia STARS, I scan that as well. My issue with STARS is the TG's seem to switch towers- at least in my area. For example: Culpeper 2 is not affiliated with Rawley Springs, Bear Den or the Harrisonburg site, all of the time. It's difficult know which site to pick to scan on STARS. In my vehicle, I scan 3 separate towers (with a Pro-197) to make sure I get the local stuff from STARS- on my 436, I stick to one because of the scan speed- if I scan STARS at all.