Moving on from Starting Strength

Let me preface this by saying that I have read the 3rd edition of Starting Strength from cover to cover, and I am still curious of this answer.

How do you guys tell when it is a good time to move on from SS/SL? I started back in October on SL5x5, ate a lot, slept a lot, did the program, and went from 150 up to around 170 (as a 5'8" 20 y/o M). My lifts went:
OHP: 65 -> 105
Bench: 85 -> 150
Row: (I don't remember where this started) -> 150
Squat: 155 -> 315
Deadlift: 135 -> 275

That was back in April. I lost access to a gym for about a month, and my lifts dropped (of course). When I started back up, I added in Cheatmode, switched to just 3x5, so basically SS, but with Pendlay rows instead of power cleans. I'm planning to cut until the end of August (at least). My lifts are going back up, and continuing to increase as I'm cutting, although very slowly.

OHP: 95 Bench: 145 Row: 145 Squat: 295 Deadlift: 265

But I'm definitely not within my noob gains anymore. Maybe it's because of my cut, but gains were starting to come slowly at the end of my bulk back in April, as well. Now I'll hit all three sets of my bench once every two or three times, so I don't have to deload according to the program, but it's very slow. I've also noticed that squatting and deadlifting in the same day is tough. I can only finish all my reps and move up in weight in whichever exercise I do first. Today, I went DL -> OHP -> Squat, and by the time I got to squats my lower back was so tired that I decided it would be better to just not do them today. When I squat first, I'm basically guaranteed to not make my deadlift's required reps.

I'm just wondering if I should deviate from SS a bit here, and how I should do it. I'll probably keep OHP, Bench, and Row on SS (maybe even start working on the form for power cleans), but I feel like squatting and DLing according to SS just won't work now.

Also, I would like to finally fix the fact that my DL is lower than my squat. I know that your immediate reaction is, "You're not squatting low enough! Use proper form!" Yeah, that's fittit's go-to answer when someone squats more than they DL. After reading through Starting Strength, though, I know what Rippetoe's standards are for a lowbar squat, and I'm fairly sure that's not the issue. I use proper lowbar position and go below parallel, getting my hips below my knees, knees following the line of the toes. I think it's just a matter of frequency and duration. I actually started squatting (with improper form, I'm pretty sure) before I learned of SS or SL, so I squatted for about a month before I started deadlifting. Also, I feel like squatting every time I lift and DLing just once or twice a week just let my squat advance faster.

Anyway, the 3rd edition of SS says that it only concerns itself with novice programming, and doesn't provide much insight into an intermediate program. That leaves me curiously unaware of where to go from here. Am I no longer a novice (at least for squat and DL)? Should I switch to a program like Madcow? Maybe I could just wait until I'm done cutting, and once I start bulking again I'll see faster linear gains again on SS?

TL;DR - Squat and DL hard to do on same day. Linear gains slow. Me not novice no more? What do!?