I had a similar situation happen on my 98 last year. It would barely crank (super slow), but it would start most of the time. So I did what any normal person would do, picked up a new battery. Low and behold that didnt fix it, and it did the EXACT same thing lol. So i replaced the starter and its been good to go ever since.

Have you tried tapping on the starter with a hammer while someone cranks it over to see if that changes anything?