Squat progression starting to stall?

[KrnxMan86]

I'm still on Phase 3 of SS, and I squatted 275 lbs for the full 3x5 the other week, and moved up to 280 lbs on the third workout. However I was only able to squeeze out 5 reps the first set, I only managed 4 then 3 on the next sets. I attempted the squat with 280 lbs again tonight, and achieved 2x5, but could only squeeze out 4 reps the third set.
Does it sound like I'm on the intermediate stage of training now since my progress is stalling? Should I move onto the HLM version of the programme?

[Steve Hill]

This is a programming question, and as such, we need all the answers to all the questions in the sticky on programming questions.