Low compression on number three, four and five cylinders

I purchased the vehicle listed above, which I thought was a jam up vehicle last Tuesday that was converted from carburetor to TBI.
This past Saturday we went on a short one hundred and thirty mile trip. On the way home I got to hearing a noise, best I could explain would be a ticking/knocking almost an exhaust coming through hole in muffler noise. As we headed up the highway on a decent incline she just fell on her face like she was only running on part of the cylinders. I pulled in store and checked the oil, it looked like oil no milky film or anything. Once you got up to speed or on flat ground it would go fine just that noise.

Yesterday I did a compression test; cylinder number one 150, number two 135, number three 90, number four 30, and number five 30. I did not even check cylinder number six due to the frustration I was already having by those last numbers. We took the valve cover off and only three of the bolts needed a wrench to loosen. Valve train looked good other than they were all so tight you could not wiggle them at all. We adjusted the tension from the top a little. Retried compression on a bad cylinder and got same number. This vehicle has a custom header on it instead of the regular exhaust manifold and no leaks or cracks are seen in it. The next verdict is that this is a head gasket blown or a warped head.