So my ECM grounds (6 I think) all read about 3.5 ohms to the battery negative.

Pretty low for small mounts of current, but not zero.

I inspected the ones I could find.

I measured the block to the battery it was also about 3.5 ohms.

Both ground straps at the back of the heads were in place and seemed secure but in a tight spot so I left them alone.

I am thinking of just adding two more jumpers myself, right to the battery using some #10 wire. Maybe even going nuts and adding new jumpers to various locations of the chassis from the battery negative. It'll be easier than lifting/cleaning the existing straps.

An thoughts? Is more better?

 

More grounds wont hurt anything but have you tried testing your leads and seeing if that is what the leads read by themselves. The odds that every ground reads the same and it is not near zero is unlikely.