Higher reps help with power, lower reps helps with strength.
You need high power and strength to get your best 1rm.
You can do high reps only, have high power, but lack strength. This will equate to, for example, being able to do a set of 5 at 315, but your 1rm is only 335.
You can do low reps to get high strength, but lack power. This will equate to, for example, your 1rm being 335, but you can only do as set of 5 at 265.
These are made up numbers.
The key is you need to do both. Higher reps will build mass, which you can turn into strength.
Generally speaking, on a 12 week cycle, a common practice is higher reps for 8 weeks, the low for 3, week off, then max out. the 3 is your peak cycle to gain strength from your mass gains.
I'm with you, I can squat heavy, but my reps suck terribly. I feel I've hit a hard stick beause of it, and next cycle I will take off the wraps and go sleeves only for 4-5 weeks, then wraps for higher reps (5 or so) for 3 weeks, then peak.