I'm trying to figure out where I am when looking to make some tweaks to my weight lifting plan. I've been doing Stronglifts on and off for several months and I'm reaching the point where I feel some extra assistance exercises or alternate workouts might help with some of my goals. From what I've read, adaption occurs differently for lifters as beginners than in intermediate or advanced stages, and thus I'm trying to figure out which category of workouts to look at. I am currently 6'2" and 230 pounds.

Bench: 260 5x5 during last Workout "A"
Squat: 275 5x5 during last Workout
Barbell Rows: 170 5x5 during last Workout "A"
OHP: 165 5x5 during last Workout "B"
Deadlift: 320 1x5 during last Workout "B"

Are you still progressing (adding weight) each workout? If so, then you are still a novice.

If not, have you reset your weights? If not, then you are most likely still a novice.

I am still progressing, though I have reset a few times on some exercises. I'm getting to the point where it is all I can do to get my reps up with 90 seconds of rest, and form is starting to get shaky on some (like starting to lean back on overhead press). Thanks

You might want to drop down to three sets of five and see how much more progress you can get that way.

Still do proper warm up sets of course.

Eta just read you are only resting 90 seconds.  That would be the problem right there.  I'm assuming you are going for strength...if that is the case you should rest as long as needed to be able to get your next set in.  On squats that can be 8-10 min for me.

This. Get your rest in.

Doesn't Stronglifts progress to 3x5? Maybe rather than reset? It's been a while since I read the info on it.

This

Drop to 3x5 and continue to progress. Invrease your reat time. The goal of Stronglifts is to get you to lift as much weight as possible not to see how fast you can lift that weight. If you want conditioning do it afterwarf or on an off day.

I watched this video and remembered the OP and this thread. I thought I'd share it.

I lifted using the Scivation triphase program for about 9 months and I added weight every workout. I switched over to starting strength and was able to add weight a little while longer. I plateaued these last few weeks and will be using 5/3/1 to continue progression.