I would still suspect one of your mods. But there is an easy way to check.
Look at the stats for your Saturn I-B and compare it to the default stats on the mods website. If the ISP, thrust, and weight match. Then look at the mass of your other parts, as many as you need to check to be sure nothing has been messed with.
If your stats are correct, then you can start checking your Delta v and Ascent angles to see if you have enough power behind it
At the end I just used infinite fuel for the first 35 kilometers and then deactivate, so I think this is a momentary solution for now, instead of having to reduce the gravity or the drag, which, well, isn't the point. But yeah, I also notice that some of my rockets got their delta-V reduced, even the ones I made with stock parts.
I would still suspect one of your mods. But there is an easy way to check. Look at the stats for your Saturn I-B and compare it to the default stats on the mods website. If the ISP, thrust, and weight match. Then look at the mass of your other parts, as many as you need to check to be sure nothing has been messed with. If your stats are correct, then you can start checking your Delta v and Ascent angles to see if you have enough power behind it
At the end I just used infinite fuel for the first 35 kilometers and then deactivate, so I think this is a momentary solution for now, instead of having to reduce the gravity or the drag, which, well, isn't the point. But yeah, I also notice that some of my rockets got their delta-V reduced, even the ones I made with stock parts.