What’s wrong with this 1964 230ci?

[Lugnutz65]

1964 Chevy 230ci inline six that’s been rebuilt about 10K miles ago by a machine shop. RV cam. I bought it from the original owner because he did a V8 swap so he could tow a trailer.
I recently removed it from my 1965 C10. I was never very happy with how it drove. Just didn’t have much power at highway speeds. I remember doing a compression test on it right after I bought it and things were fine and oil pressure was good too.

Update. I put the 230ci on my engine run stand so that I could show it running and sell the engine for a fair price. Oil pressure checked out great. Starts right up. Cylinder compression check is 130 psi in all cylinders.

Today I ran a cylinder leak down test on this engine. Disappointing results. I didn’t bother testing all of the cylinders because cylinders #3, #4, #5, and #6 all had leak down numbers of at least 50%.
To run the test I loosened all of the rockers so the valves were all closed. At first I thought I had terrific numbers but realized that the hose I was using still had a Schrader valve in it. Haha, joke is on me. After I removed the Schrader valve, I was shocked to see 50% leak down. I tested all of the cylinders listed above. My heart sank. No air out the exhaust or from the carburetor.

So I have concluded that the air is getting past the rings. I had been using this engine in my 1965 C10, but was never impressed with how it ran. Maybe this is why.
I put new valve seals on the exhaust valves #5 and #6. I had those springs off to check for sloppy valve guides, but they were fine. Absolutely no wobble.
I rotated the crank to find the base circle on the cam for each cylinder and reset the lash properly for each valve. The engine starts and runs.
I tested my leak down tool by hooking up 100 psi from my compressor without connecting it to the engine. Both sides show 100 psi as you see in the picture. I think my leak down tool is working properly.
Does anyone think my conclusions are wrong?