The performance shown seems pretty legit to me. I gave it a try, I could escape the Solar system:
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That was without payload and by spending all the fuel, but it looks honest.
However that rocket can be optimized.
TheStolenInvestigator you use too much engines on your first stage. Have a look:
View attachment 42125
The main engine alone is enough to lift the rocket.
That's still without payload. With a payload it's barely enough, but by making a few optimizations it's easy to alleviate it. Have a look:
View attachment 42126
I removed the 2 Hawk engines and the hidden fuel tanks on the first stage, and I replaced the second stage engine by a Frontier, which is way more efficient. I made the second stage longer but that's only to compensate for the hidden fuel tanks that I had to remove. And even with a payload, now the TWR is acceptable.
Now look if I run a test:
View attachment 42129
That's just before separation, I left 10% of fuel in the first stage:
View attachment 42130
Then to orbit:
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And beyond:
View attachment 42133
That's with a payload (37.5t), and after having left some fuel in the first stage.
If I burn the 1st stage until the end, here is what I end with:
View attachment 42136
See? Much better! That rocket can still be optimized. Also, always make a try with your build, if possible with a payload at full capacity. That way you will have an accurate idea about your rocket's real capacity