I have been on TRT for 2.5 years now, and I also notice the same thing.  I actually just thought of this today.  I haven't been drinking much coffee in the last 2-3 months, but just started having cups recently so I should be wired off it, but I barely feel anything from it now.  I would also say that any euphoria induced from the stimulants is also greatly reduced, if not almost entirely eliminated.  It's actually a little concerning, since it may indicate either adrenal fatigue or perhaps some sort of neurotransmitter receptor downregulation.  I also even notice in general that I don't get as excited about things as I once did.  I am going to play around with my protocol here replacing some of my daily test cyp with test prop to try and invoke some fluctuations to give the androgen receptors a break on a regular basis.  I'm starting to wonder if keeping testosterone levels sky high 24/7 with daily injections of cypionate is a good thing or a bad thing for overall wellbeing.