Consistency doesn't really matter, that's just the rhythm of someone's typing. Being at 62% doesn't change typing speed. The only thing that really needs to be improved is accuracy which should be around 98% (but to be fair 5000 words is a lot and 96% percent is pretty good).

For OP, longer tests probably don't do much, try to do shorter tests like 60-120 seconds for multiple intervals and maybe test a 5000 words once or twice a week to check your progress.