I'll go wtih the tough beard angle and advise from there (saying ahead of time I've been at it less time than some fo those already responded).

my beard is fairly coarse, and my skin very sensitive. I found that just the addition of putting lather on my face and letting it stand while I stropped my razor, then wipe off with hot towel and put on fresh warm lather made a big difference for me. I have a coworker who uses mach 3's and he asked me about razor burn he was having, I suggested he do the same thing with his conventional foam. asked him 2 weeks later, he says it has helped.

other things that might matter, the blade itself, I had one razor that was definitely sharp enough, but did not give me a good shave. different blades for different faces and beards. if you do send yours out for sharpening, as the person that hones it to strop it as well. shave with it as it arrives, then if you strop and there is a diffeence in the shave, you are stropping wrong.

and off and on you've been shaving, have you been varying your technique throughout, to find the right angle and motion? One thing I did that helped me was film myself, I then watched it and noticed things I was doing I needed to chagne. specifically I would sometimes go over an area I had already shaved without putting on more shaving cream. with youtube you can even post it and get feedback from forum members.

are you going against the grain? try shaving just with the grain, and across, but not against. see how you do.

I recommend not giving up. I honest didn't notice a difference in smoothness from the straight and the mach 3, but I have noticed less irritation. I can't imagine that with the right tools in the right condition and the right technique you can't get a good shave.

Red