I'll say this:
1. at 35, you're definitely out of your "metabolic golden years". You are also like at or very close to a significant metabolic slowdown. Its common around 35 or so, though can come much later or much earlier for different people. Its not the end of the world as you can be in great shape for the rest of you life, just going to take more recovery and less volume than you used to do.
2. If you are doing the Stronglifts 5x5 with the specific intention of getting stronger, you need to eat more. It is really difficult to increase strength considerably without a *surplus* of calories. Realistically, you probably need another 1,000 calories a day to effectively support that program.
3. 9 hours of sleep is good. 10 is better. 8 is absolute minimum. The older you get, the more important this will become. Note these are hours of sleep not hours laying in bed.
4. I did a similar linear progression strength program back in Jan and Feb. I'm 6'1/ 190#, 40 years old, so very similar stats. I was putting down about 4,000 calories a day including a half a gallon of whole milk. I put on about 8 lbs during the cycle and my backsquat increased 75 pounds. I've since lost 8 pounds and backsquat dropped back down 30-40 lbs as I haven't been eating as much and doing much more conditioning volume. Anyway, during the strength cycle, I did 2 HIIT sessions per week on recovery days from the strength sessions. These were short, 15 minute sessions that involved movements that would not impede recovery: Double Unders, KB swings and rowing sprints. Pushing the prowler around in short bursts or an Assault Bike or Ski Erg (if you have access to them) can be good, too. Doing a 5x5 linear progression strength cycle, especially beyond your 20s, you're just going to be limited to how much conditioning volume you can effectively do. Sure, you can do a lot of conditioning -the temptation is to do as much as you are capable of squeezing in, but the real question is one of effectiveness. on 5x5 program, your backsquat should be seeing an increase of 10# per week. This is significant, but also the reason you do a program such as this.
If you are not seeing that, then some combination of insufficient sleep, too much volume, insufficient calories, insufficient recovery is at fault.
The most important thing to keep in mind is that you are not getting stronger, faster or increased endurance when you are working out. You get stronger, faster and more endurance when you are sleeping and eating. The training is the stimulation for that recovery and improvement to take place. Recovery is more important than the actual workout. Treat your sleep and eating with at least as much attention as you do your actual training.