well i have an obby mauler and it has 5 attack.
now if ure 1 range, i suggest u to cannon hard/multi area tasks until u reach the limit where ure not range based, if the limit is reached and u still havent got 55 slayer, start doing tasks with mage(u need 50 mage to wear the staff) so yeah ull get it while doing tasks with mage, and if u max out the mage and range limit and still have some slayer xp or lvls to get, this is where 5 attack(also great for staking!) will be needed because with 1 attack it will be like 20-30% slower.
also i suggest u to do one small favour quest(20kxp on ur choice) and varrock museum minigame(search it in google) which gives some xp which is pretty decent for slayer.
also if u would like to afk crabs, try waterbirth island.
btw if u bot then u can bot at slayer tasks(less botobvious).
Goodluck on ur goal brah
i would also recommend not dismissing Exam and Genie Random Events because they give xp lamp/book of knowledge which is pretty decent xp for slayer and u an get tons of slayer xp while doing other activity.