The problem described in BZ 174336 and 185781 still exists in RHEL 3 U9, with initscripts-7.31.31.EL-1. As described in those tickets, reconfiguring the network from a "screen" session, and doing this in a screen window other than window 0, you will get a random, small TCP window size set for your default route. Pretty hard to track down, and easy to fix - by backporting the one-line change from BZ 174336 to RHEL 3.
I don't think this fits the RHEL 3 criteria at this point, though. Feel free to raise via the appropriate TAM/PM/etc.