P-29, I feel your pain! I had my drive looked at in March. It needed to be rubuilt. VERY long story turned VERY short, I got my boat back July 10th. It is 60* and cloudy here today so I am typing this instead of boating.
I am turning about 4700 rpms and about 75mph depending on conditions. I am hoping that having my props worked will get me closer to 5000 rpm. I installed longer K-planes on my boat which did scrub 1-2mph but they made the boat handle much better in slop so it was a fair trade.
I was leaning toward Mercury too but Sarasota Hill actually did a few blackhawk props for the 22 Classic so they have some good experience with my boat and what needs to be done.
A bad ground on your battery made your transom turn black? I didn't know a bad ground on your battery could cause a boat to run rich. Good to know.
I see your from MI too so you know how it is!