RE: sticking point
IME, i try to get a full warm up with lots of reps during the very first light sets, then go up with much less reps like 2 to 5 before working sets so as to spare energy, making quite big jumps in the begining. I also try not to completly recover between sets, make it quick. I think doing my sets fast makes me burn less gas than taking time to fully recover thinking this would help me spare my energy. I know it sounds a bit daft but with time i get more effective at it.
To sum it up, i find you dont warm up enough and get too many reps on sets are are too close to your working ones.
Concistancy in a given intensity is what pays most imo.
You can squat 140kg, lets assume it is for 1 rep, i'd go for 5 working sets of 3 to 5 reps each at 80/85% (112.5/120kg) depending on how you feel and what you just did before. Then i'd try to build up from there, starting with sets of 5@120kg if possible during a couple of weeks then switch to 3's@125/130k, then 2's maybe...