IMHO, Tmax400 in Rodinal is just a waste of a very good film in an unsuitable developer.
I have to agree with GeorgK on this one. Many years ago I tried Rodinal with Tri-X and wound up with contrasty, grainy negatives when exposed at box speed. I don't want to start a war on this issue but from my experience, Rodinal (which I do use for some applications) is not the panacea that some make it to be. For ease of use, I have been personally satisfied with HC-110 dil B (1:31). Temperature control is easy and have been using it for TMY, TMX, Across and sometimes even the Foma films. It's also very cheap as well. My runner-up developer is Xtol. It's bit more costly and I use it 1:1 dilution (which I gather the OP wanted to escape from since he's using D-76 1:1). My advice--either change films (Across is OK with Rodinal) or switch developers.