Definitely sounds more like you are just hitting a mental plateau to your running rather than anything physical. I hit a bit of a wall like that when my runs started creeping up above 8km or so. Found it hard to get out there every day and was coming up with little niggling injuries to stop running.
I got through it by modifying my running schedule to include more "fun" sessions, like fartlek runs, repetitions and hill work instead of just plodding along at the same pace constantly.
Looking at the tough mudder training you've got above, it looks like it only asks for 2 runs per week dor most of the training program, then kicking up to 3 a week for the last 4 weeks, so my suggestion would be to keep doing the hills sessions, then if you really aren't liking the long runs perhaps substitute some more speed work with some long repetitions or a fartlek session.
Something like jog 10 mins warm up, then 4 x 1km repetitions with a 2 min rest in between, then 10 min cool down. That will still see you running a good 6-8km depending on what sort of pace you run at for your warm up/cool down.
Or just do a fartlek session, which is basically switching between hard running and joggin over set time periods. Again 10 min warm up, then run 2 x 90 sec, 4 x 60 sec, 4 x 30 sec, 4 x 15 sec, jogging for the same amount of time between each rep (so 90 sec jog between the 90 sec reps etc), then 10 min cool down jog. This will also see you run 6-8km depending on your speed.
They are 2 really good speed sessions that will also assist your distance running, and are a little more fun to complete than just running along at a set pace. Realistically though running is never going to be fun.... I saw a running shirt the other day that said "My sport is your sports punishment", which sums it up pretty well