Diagnostic question

I have a stumper that someone here (RRR) will know the answer to.

I have a 5.9 Magnum in my Dart, dead stock, hooked to a 4-speed.

I missed a shift. The next day, when cranking, it sounded like a cylinder or two were out on compression when cranking. wha-wha-WHA-wha-wha kinda thing. Seemed down on power but had no funny noises.

I pulled the valve covers and rocker arms expecting to find bent valves. Pushrods were all straight, and there was some variance in the heights of the valves but nothing major. With the rockers off, I pressurized the cylinders with air via leakdown tester. Six cylinders were at 10%, 2 were at 15%. This blows up my theory about valves and/or pushrods.

Any ideas? Anyone?