A leakdown test can tell you pretty definitively if it's the rings. My guess is that, yes, it probably is. If the heads were less than tight before, you've just corrected that and in theory, increased internal cylinder pressure. It leaks past the rings, and the reverse is true during the intake stroke of the engine. More oil can be drawn into the cylinder past the rings since the engine is a little better at generating the vacuum that draws in the intake charge. This used to be a "given" on small block Chevy's after doing a head job...the rings would be the next weak link.

All that being said, oil is cheap.

John B.