I was also extremely disappointed in XTOL when I tried it last year (mostly with TMX). I had borderline underdevelopment right off the bat (and I mixed, diluted, timed, and agitated VERY carefully per Kodak's instructions - I used to be a pro and I've been doing this since the sixties), and the solution become exhausted in a matter of weeks. Despite constantly increasing my dev time, I never got a truly good roll.(posted 8930 days ago)The closest-to-good negs I got on the first roll did show promise. The TMX did come out a little finer-grained than in D-76, and, more importantly, with the inherently high contrast somewhat tamed. But I grew tired of ruining roll after roll, and eventually I went back to D-76...
Personally, my gut feeling is that the newer products like TMX and XTOL really demand the extremely precise metering/exposure of modern cameras and extremely precise temp-control and agitation of machine processing. Using our old match-needle Nikons and small tanks, I consistently get much better results with old standbys like PX and TX in D-76. (And since I also happen to much prefer the look of the old films, this isn't really a tragedy.)
I'm sure if I continued in a concerted effort I could get the XTOL/TMX combo to work better for me... Maybe I will sometime, but for now I think I'll stick with the classics, which (due to Kodak's quiet incremental improvements over the years) also happen to produce better results than ever.