96 truck. Always started great and then last week it started cranking noticeably slower. Still started but the first revolution has a hesitation and then it spins but slower than normal. Replaced both batteries and checked the grounds with an ohm meter. Checked the connection on the starter and it was a little loose so tightened it up. The only thing I can think of is the starter, which was replaced 10,000 miles ago, has gone bad. Am I missing something before I go down that path?

 

-Your batteries have the appropriate CCAs, right?
-Check the ground on the starter with an ohm meter

Those are the only things I can think of off the top of my head.

 

Do you have a lot of corrosion on your battery cables? If so, this can cause slower cranking.

Did this start suddenly or over a little time?

A really old starter won't crank an engine over as fast but I doubt you have enough starts to have worn out the internals.

 

Batter terminals are clean and bright. Did not check the ground from the starter to the block. Will do that today. Slow crank just started all of a sudden. New batteries are 800 cold cranking amps which I think is up to spec.

 

The starter grounds itself at the block. You could try to shine up the Mating surfaces of the starter and the block if you get any resistance between the starter case and the block.

 

i chased a hard starting issue that sounds like yours, ended up being my starter.

 

I just went down the same road, turned out to be loose/corroded cables. Took the starter apart for fun to clean it up and look. It was nasty inside.