Methylphenidate brand inconsistent?

Hello everyone, I'm 38 and just got diagnosed with combined type 2 months ago. So I've been on ritalin ir, but I was wondering other people's experiences? The generic brand I have is kvk tech, but it seems wildly inconsistent. Even though I've been keeping the variables I can control like sleep and diet the same. One day it'll help tremendously with executive dysfunction and make me slightly calmer and then the the next day, nothing. Another day it'll last for 4 hrs and the next day it'll last for 2. I was upped this month, but this prescription is just weird. I felt some effects once that were very intense, but since then, nothing. And the higher dose gives me cold fingers, high bp, and a terrible crash, but thats even when I get 0 good effects from it. So I had some of the lower dose left so I went back to that and it was better but they're inconsistent. And today since I'm almost out of the lower dose I broke a bigger dose in half and a a low dose in half since they're scored and took that and even 1 hr into my 2nd dose I feel a heavy crash and my fingers and toes got really cold and I don't feel any difference. And this is the first time I've had 1 of the higher dose since last week and i hadn't had the cold fingers since then, but even in half it's still doing this. So my question is, is there a better generic brand that actually works well, consistently? This is just aggravating. Maybe i should ask my Pysichiatrist if i could try Teva? I hear they're a good generic. Thank you.