Did you follow the starter alignment instructions when you replaced the starter? Are you getting oil on the Bendix? That could cause the starter gear to engage slowly. It is possible that the replacment starter has a problem. Also, if the previous starter had the same problem it could have damaged the gear on the flex plate.
check ecm fuse
Dirty fuel filters are a huge cause of this especially on diesels, I have replaced 3 this week all with the same symptoms. also check that the fuel pump is working. if it is trying to turn over,but it can't, you either have a bad starter,or a seized engine
the solenoid on your starter is finished, replace the starter......
Could be a bad battery or starter.
BAD STARTER OR TIMING OFF LEAKING FLOATS
Does the engine crank over?
Most commonly, it's the starter or the starter was wired wrong when it was installed. More rarely, it can also be the keyswitch or even a bad gear on the flex-plate.
Sounds like a failed starter.
the starter may not be good or the connection on the starter may be loose
Try an ignition switch.
If it's not cranking at all, you probably forgot to connect a wire, or you replaced the wiring incorrectly.
There are several things that can cause everything to go dead when you bump the starter. The most common cause will be a loose or corroded ground wire.